Guile-ICS Reference Manual

For Guile-ICS 0.5.0

Artyom V. Poptsov

This manual documents Guile-ICS version 0.5.0.

Copyright (C) 2017-2022 Artyom V. Poptsov

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”

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The Guile-ICS Reference Manual

This manual documents Guile-ICS version 0.5.0.

Copyright (C) 2017-2022 Artyom V. Poptsov

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License.”


1 Introduction  
2 Installation  
3 API Reference  
4 Tools   
Appendices
Appendix A GNU Free Documentation License   The license of this manual. 









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1 Introduction



Guile-ICS is a GNU Guile
library that provides API for iCalendar
RFC5545 format parsing.








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2 Installation



Guile-ICS sources are available form GitHub at
https://github.com/artyom-poptsov/guile-ics.  This section
describes Guile-ICS requirements and installation process.



Guile-ICS depends on the following packages:









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2.1 GNU Guix





$ guix install guile-ics









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2.1.1 Development version




$ guix build -f ./guix.scm
$ guix package -f ./guix.scm









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2.2 Manual Installation



To build the latest version of Guile-ICS from the sources, you need to
download the sources from GitHub or clone them using Git(1).



Cloning can be done as follows:





$ git clone git@github.com:artyom-poptsov/guile-ics.git




Next, you should configure the sources:





$ cd guile-ics/
$ autoreconf -vif
$ ./configure




And finally build and install the library:





$ make
$ make install




For a basic explanation of the installation of the package, see the
‘INSTALL’ file.



Please note that you will need
Automake version 1.12 or
later to run self-tests with make check (but the library
itself can be built with older Automake version such as 1.11).



important You probably want to call configure with
the ‘--with-guilesitedir’ option so that this package is
installed in Guile’s default path.  But, if you don’t know where your
Guile site directory is, run configure without the option,
and it will give you a suggestion.








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3 API Reference



This chapter describes the Guile-ICS API.  The first thing that should
be discussed are iCalendar streams.








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3.1 iCalendar streams



Main module for Guile-ICS is (ics).  The module contains main
procedures for reading and writing iCalendar data.



The data comes in the form of iCalendar streams: these streams consist
of one or more iCalendar objects (described in the next section.)



Example of an iCalendar stream of one iCalendar object from RFC5545,
section 3.4:





BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
UID:19970610T172345Z-AF23B2@example.com
DTSTAMP:19970610T172345Z
DTSTART:19970714T170000Z
DTEND:19970715T040000Z
SUMMARY:Bastille,Day\,Party
X-WR-TIMEZONE;VALUE=TEXT:Europe/Brussels
END:VEVENT
END:VCALENDAR




Let’s assume that this iCaneldar object is written in a file
‘example.ics’, then we can convert it to a Scheme representation
using ics->scm procedure:





(ics->scm (open-input-file "example.ics"))
⇒ (#<ics-object VCALENDAR 23cf630>)




The procedures below can be used to convert iCalendar streams to Scheme
lists of iCalendar objects and vice versa.








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3.2 Guile-ICS Main Classes








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3.2.1 <ics-content>



A common class that represents generic iCalendar contents.  The class is
defined in (ics content) module.








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3.2.1.1 Fields





Init KeywordTypeDescription


#:name<string>The name of an iCalendar content.










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3.2.1.2 Public Methods





Method: ics-content-name ics-content


Returns the name of a ics-content object.









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3.2.1.3 Miscellaneous Procedures





Scheme Procedure: ics-write-line obj [port=(current-output-port)]


Display an obj to a port with CRLF line ending.






Scheme Procedure: ics-format dest fmt . arg


Write output specified by a fmt string to a destination dest
with CRLF line ending.






Scheme Procedure: scm->ics-value value


Convert a value to iCalendar format string.  value can be
either a list of strings or a string.









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3.2.2 <ics-object>



iCalendar object (see RFC5545, section 3) stores calendaring and
scheduling information.  iCalendar object class consists of a sequence
of calendar properties and one or more iCalendar component. Each
component is an iCalendar object (that is, instances of
<ics-object> class) on its own; that means that this data
structure can be handled recusively.



The class is defined in (ics object) module.








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3.2.2.1 Fields





Init KeywordTypeDescription


#:properties<list>iCalendar object properties (instances of <ics-property> class).


#:components<list>iCalendar components (see RFC5545, section 3.6.).
Components are instances of <ics-object> class themselves.










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3.2.2.2 Public Methods





method: ics-object-name ics-object


Return an ics-object name.






method: ics-object-properties ics-object


Return an ics-object properties list.






method: ics-object-property-ref ics-object name


Return an ics-object property value by a name.






method: ics-object-components ics-object


Return an ics-object components list.






method: ics-object->ics ics-object port


Convert an ics-object to a iCalendar format and print the result
to a specified port.









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3.2.3 <ics-property>



A property is the definition of an individual attribute describing a
calendar object (see RFC5545, section 3.5.)  Since Guile-ICS tries to
unify the way of handling iCalendar information, iCalendar property
class is used for both iCalendar objects (as defined in RFC5545) and for
components of iCalendar objects.



The class is defined in (ics type property) module.








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3.2.3.1 Fields





Init KeywordTypeDescription


#:type<symbol> || #fiCalendar type name as described in RFC5545, 3.2.20.


#:value<string>iCalendar property value.


#:parameters<alist>iCalendar property parameters (see RFC5545, section 3.2.),
stored as an association list.










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3.2.3.2 Public Methods





method: ics-property? x


Check if x is an instance of <ics-property>, return
#t if it is, #f otherwise.






method: ics-property-type ics-property


Get the type of an ics-property.






method: ics-property-name ics-property


Return an ics-property name.






method: ics-property-value ics-property


Return an ics-property value.






method: ics-property-parameters ics-property


Return an ics-property parameters association list.






method: ics-property-parameter-ref ics-property name


Return an ics-property value for a parameter with a given
name.  Return #f if no parameter found.






method: ics-property-parameter-set! ics-property name value


Set an iCalendar ics-property parameter name to a
value.






method: ics-typed-property->ics-property ics-property


A generic method.  Convert an ics-property to an untyped version.
For <ics-property> this methods bascally does nothing and returns
ics-property as is.









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3.2.3.3 Miscellaneous Methods



These procedures are defined in (ics type property).





Method: ics-property-determine-type ics-property


Determine the type of an ics-property, return the type as a
symbol.






method: ics-property->string ics-property


Convert an ics-property to an iCalendar string, return the string.






method: ics-property->typed-property ics-property


Convert a generic ics-property to a typed version of itself;
return a new typed property.









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3.2.4 <ics-stream>



The class is defined in (ics stream) module.








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3.2.4.1 Fields





Init KeywordTypeDescription


#:source<port> || <string>iCalendar data source.


#:parse-types?<boolean>Should the parser parse the types?










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3.2.4.2 Public Methods





method: ics-stream-source ics-stream


Return a source of an ics-stream.






method: ics-stream-parser ics-stream


Make a new iCalendar stream parser for an ics-stream, return a
new parser.






Method: ics-stream-parse-types? ics-stream


Return #t if the parser should parse the iCalendar types,
#f otherwise.






method: ics-stream->scm ics-stream


Convert an ics-stream to a Scheme list of iCalendar objects
(<ics-object>).  Return the list.






method: ics-stream->scm-stream ics-stream


Convert an ics-stream to a SRFI-41 stream.  Return the stream.









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3.3 Guile-ICS Property Types








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3.3.1 <ics-property:binary>



The class is defined in (ics type binary) module.








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3.3.1.1 Public Methods





method: ics-property:binary? x


Check if x is an instance of <ics-property:binary>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:binary property


Convert a property to a its typed version.






method: ics-property:binary-encoding property


Get binary encoding for a property.  The encoding value is either
"8BIT" (RFC2045) or "BASE64" (RFC4648).









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3.3.2 <ics-property:boolean>



The class is defined in (ics type boolean) module.








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3.3.2.1 Public Methods





method: ics-property:boolean? x


Check if x is an instance of <ics-property:boolean>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:boolean property


Convert a property to a its typed version.









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3.3.3 <ics-property:cal-address>



The class is defined in (ics type cal-address) module.








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3.3.3.1 Public Methods





method: ics-property:boolean? x


Check if x is an instance of <ics-property:cal-address>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:cal-address property


Convert a property to a its typed version.









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3.3.4 <ics-property:date>



The class is defined in (ics type date) module.








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3.3.4.1 Public Methods





method: ics-property:date? x


Check if x is an instance of <ics-property:date>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:date property


Convert a property to a its typed version.









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3.3.5 <ics-property:date-time>



The class is defined in (ics type date-time) module.








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3.3.5.1 Public Methods





method: ics-property:date-time? x


Check if x is an instance of <ics-property:date-time>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:date-time property


Convert a property to a its typed version.









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3.3.6 <ics-property:duration>



The class is defined in (ics type duration) module.








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3.3.6.1 Public Methods





method: ics-property:duration? x


Check if x is an instance of <ics-property:duration>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:duration property


Convert a property to a its typed version.









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3.3.7 <ics-property:float>



The class is defined in (ics type float) module.








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3.3.7.1 Public Methods





method: ics-property:float? x


Check if x is an instance of <ics-property:float>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:float property


Convert a property to a its typed version.









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3.3.8 <ics-property:integer>



The class is defined in (ics type integer) module.








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3.3.8.1 Public Methods





method: ics-property:integer? x


Check if x is an instance of <ics-property:integer>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:integer property


Convert a property to a its typed version.









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3.3.9 <ics-property:period>



The class is defined in (ics type period) module.








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3.3.9.1 Public Methods





method: ics-property:period? x


Check if x is an instance of <ics-property:period>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:period property


Convert a property to a its typed version.









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3.3.10 <ics-property:recur>



The class is defined in (ics type recur) module.








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3.3.10.1 Public Methods





method: ics-property:recur? x


Check if x is an instance of <ics-property:recur>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:recur property


Convert a property to a its typed version.









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3.3.11 <ics-property:text>



The class is defined in (ics type text) module.








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3.3.11.1 Public Methods





method: ics-property:text? x


Check if x is an instance of <ics-property:text>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:text property


Convert a property to a its typed version.









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3.3.12 <ics-property:time>



The class is defined in (ics type time) module.








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3.3.12.1 Public Methods





method: ics-property:time? x


Check if x is an instance of <ics-property:time>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:time property


Convert a property to a its typed version.









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3.3.13 <ics-property:uri>



The class is defined in (ics type uri) module.








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3.3.13.1 Public Methods





method: ics-property:uri? x


Check if x is an instance of <ics-property:uri>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:uri property


Convert a property to a its typed version.









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3.3.14 <ics-property:utc-offset>



The class is defined in (ics type utc-offset) module.








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3.3.14.1 Public Methods





method: ics-property:utc-offset? x


Check if x is an instance of <ics-property:utc-offset>, return
#t if it is, #f otherwise.






method: ics-property->ics-property:utc-offset property


Convert a property to a its typed version.










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3.4 iCalendar to Scheme converters





Scheme Procedure: ics->scm [port=(current-input-port)]


Convert a iCalendar stream from a port to a Scheme representation;
return a list of iCalendar objects.






Scheme Procedure: ics-string->scm str


Convert an iCalendar string str to a Scheme representation; return
a list of iCalendar objects.






Scheme Procedure: scm->ics ics-object [port=(current-output-port)]


Convert an ics-object to iCalendar format.  Print the output to a
port.






Scheme Procedure: scm->ics-string ics-object


Convert an ics-object to an iCalendar format string; return the
string.






Scheme Procedure: ics->stream [port (current-input-port)]


Convert an ICS stream from a port to an SRFI-41 stream
(see SRFI-41 in The GNU Guile Reference Manual).  Return the
stream.



Example:





(use-modules (srfi srfi-41)
             (ice-9 pretty-print)
             (ics))

(let ((p (open-input-file "data.ics")))
  (stream-for-each (lambda (ics-object)
                     (pretty-print ics-object))
                   (ics->stream p)))












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3.5 Extra Converters



(ics conv) module provides procedures for converting iCalendar
objects to other formats.





Scheme Procedure: ics-object->org-mode ics-object [port=(current-output-port)]


Convert an ics-object to org-mode format (see Top in Org Mode Manual) and print the results to a port.









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3.6 Miscellaneous Methods and Procedures



Those methods and procedures are available from (ics) module.





Method: ics-describe x


Describe iCalendar content in a human-readable form.  Return value is
undefined.






Scheme Procedure: ics-pretty-print ics-object [port=(current-output-port)] [#:indent=2] [#:show-types?=#f]


Pretty-print an ics-object to a port.  Note that the output
is intended for human to comprehent, not to a machine to parse.






Scheme Procedure: ics-debug-set! enabled?


Enable or disable debug mode for the library.









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3.7 Examples



See the ‘examples’ directory.








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3.8 Finite-State Machine (FSM)



The (ics fsm) module contains an implementation of a FSM that
parses iCalendar data.





Scheme Procedure: ics-token-begin? x


Check if an x is the beginning of an IANA token.






Scheme Procedure: ics-token-end? x


Check if an x is the ending of an IANA token.






Scheme Procedure: ics-calendar-object? x


Check if x is a iCalendar object.






Scheme Procedure: fsm-read-property parser


Read iCalendar property using a parser.






Scheme Procedure: fsm-skip-property parser


Skip current iCalendar property using a parser.






Scheme Procedure: fsm-read-ical-object parser object-name icalprops component


Read an iCalendar object object-name from an iCalendar stream
using a parser.  Return an object with iCalendar properties
ical-props and a component list.






Scheme Procedure: fsm-read-ical-stream parser result


Read iCalendar stream using a parser, return a list of
<ical-object> instances.









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3.9 Version



(ics version) contains procedures that allow to acquire
information about the Guile-ICS version in the
Semantic Versioning format.



Guile-ICS version consists of three parts: MAJOR.MINOR.PATCH



The procedures below allow to get any of the version part or the version as a
whole.






Scheme Procedure: ics-version


Return the Guile-ICS version as a list of the following form:



lisp
'(MAJOR MINOR PATCH)









Scheme Procedure: ics-version/string


Get the raw Guile-ICS version as a string.






Scheme Procedure: ics-version/major


Get the “MAJOR” part of the Guile-ICS version.






Scheme Procedure: ics-version/minor


Get the “MINOR” part of the Guile-ICS version.






Scheme Procedure: ics-version/patch


Get the “PATCH” part of the Guile-ICS version.









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4 Tools



There is a tool called ics that allows to handle iCalendar
data.



The default behaviour of the program is to read a iCalendar stream from
stdin and pretty-print it to the stdout.



See ics --help for usage information.








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Appendix A GNU Free Documentation License



Version 1.3, 3 November 2008






Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/

Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.




    

  1. 
PREAMBLE


    The purpose of this License is to make a manual, textbook, or other
functional and useful document free in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.

    

    This License is a kind of “copyleft”, which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft
license designed for free software.

    

    We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.

    

  2. 
APPLICABILITY AND DEFINITIONS


    This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License.  Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein.  The “Document”, below,
refers to any such manual or work.  Any member of the public is a
licensee, and is addressed as “you”.  You accept the license if you
copy, modify or distribute the work in a way requiring permission
under copyright law.

    

    A “Modified Version” of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.

    

    A “Secondary Section” is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document’s overall
subject (or to related matters) and contains nothing that could fall
directly within that overall subject.  (Thus, if the Document is in
part a textbook of mathematics, a Secondary Section may not explain
any mathematics.)  The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.

    

    The “Invariant Sections” are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License.  If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant.  The Document may contain zero
Invariant Sections.  If the Document does not identify any Invariant
Sections then there are none.

    

    The “Cover Texts” are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License.  A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.

    

    A “Transparent” copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters.  A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text.  A copy that is not “Transparent” is called “Opaque”.

    

    Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input
format, SGML or XML using a publicly available
DTD, and standard-conforming simple HTML,
PostScript or PDF designed for human modification.  Examples
of transparent image formats include PNG, XCF and
JPG.  Opaque formats include proprietary formats that can be
read and edited only by proprietary word processors, SGML or
XML for which the DTD and/or processing tools are
not generally available, and the machine-generated HTML,
PostScript or PDF produced by some word processors for
output purposes only.

    

    The “Title Page” means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page.  For works in
formats which do not have any title page as such, “Title Page” means
the text near the most prominent appearance of the work’s title,
preceding the beginning of the body of the text.

    

    The “publisher” means any person or entity that distributes copies
of the Document to the public.

    

    A section “Entitled XYZ” means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language.  (Here XYZ stands for a
specific section name mentioned below, such as “Acknowledgements”,
“Dedications”, “Endorsements”, or “History”.)  To “Preserve the Title”
of such a section when you modify the Document means that it remains a
section “Entitled XYZ” according to this definition.

    

    The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document.  These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.

    

  3. 
VERBATIM COPYING


    You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License.  You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute.  However, you may accept
compensation in exchange for copies.  If you distribute a large enough
number of copies you must also follow the conditions in section 3.

    

    You may also lend copies, under the same conditions stated above, and
you may publicly display copies.

    

  4. 
COPYING IN QUANTITY


    If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document’s license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover.  Both covers must also clearly and legibly identify
you as the publisher of these copies.  The front cover must present
the full title with all words of the title equally prominent and
visible.  You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.

    

    If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.

    

    If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.

    

    It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.

    

  5. 
MODIFICATIONS


    You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it.  In addition, you must do these things in the Modified Version:

    

      

    1. 
Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document).  You may use the same title as a previous version
if the original publisher of that version gives permission.


    2. 
List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has fewer than five),
unless they release you from this requirement.


    3. 
State on the Title page the name of the publisher of the
Modified Version, as the publisher.


    4. 
Preserve all the copyright notices of the Document.


    5. 
Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.


    6. 
Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.


    7. 
Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document’s license notice.


    8. 
Include an unaltered copy of this License.


    9. 
Preserve the section Entitled “History”, Preserve its Title, and add
to it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page.  If
there is no section Entitled “History” in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.


    10. 
Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on.  These may be placed in the “History” section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.


    11. 
For any section Entitled “Acknowledgements” or “Dedications”, Preserve
the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.


    12. 
Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles.  Section numbers
or the equivalent are not considered part of the section titles.


    13. 
Delete any section Entitled “Endorsements”.  Such a section
may not be included in the Modified Version.


    14. 
Do not retitle any existing section to be Entitled “Endorsements” or
to conflict in title with any Invariant Section.


    15. 
Preserve any Warranty Disclaimers.

    


    If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant.  To do this, add their titles to the
list of Invariant Sections in the Modified Version’s license notice.
These titles must be distinct from any other section titles.

    

    You may add a section Entitled “Endorsements”, provided it contains
nothing but endorsements of your Modified Version by various
parties—for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.

    

    You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version.  Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity.  If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

    

    The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.

    

  6. 
COMBINING DOCUMENTS


    You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.

    

    The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy.  If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.

    

    In the combination, you must combine any sections Entitled “History”
in the various original documents, forming one section Entitled
“History”; likewise combine any sections Entitled “Acknowledgements”,
and any sections Entitled “Dedications”.  You must delete all
sections Entitled “Endorsements.”

    

  7. 
COLLECTIONS OF DOCUMENTS


    You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

    

    You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.

    

  8. 
AGGREGATION WITH INDEPENDENT WORKS


    A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an “aggregate” if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation’s users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.

    

    If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document’s Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.

    

  9. 
TRANSLATION


    Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections.  You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers.  In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.

    

    If a section in the Document is Entitled “Acknowledgements”,
“Dedications”, or “History”, the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.

    

  10. 
TERMINATION


    You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License.  Any attempt
otherwise to copy, modify, sublicense, or distribute it is void, and
will automatically terminate your rights under this License.

    

    However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
60 days after the cessation.

    

    Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.

    

    Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License.  If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.

    

  11. 
FUTURE REVISIONS OF THIS LICENSE


    The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time.  Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns.  See
http://www.gnu.org/copyleft/.

    

    Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License “or any later version” applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation.  If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.  If the Document
specifies that a proxy can decide which future versions of this
License can be used, that proxy’s public statement of acceptance of a
version permanently authorizes you to choose that version for the
Document.

    

  12. 
RELICENSING


    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works.  A
public wiki that anybody can edit is an example of such a server.  A
“Massive Multiauthor Collaboration” (or “MMC”) contained in the
site means any set of copyrightable works thus published on the MMC
site.

    

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.

    

    “Incorporate” means to publish or republish a Document, in whole or
in part, as part of another Document.

    

    An MMC is “eligible for relicensing” if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.

    

    The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.

    






ADDENDUM: How to use this License for your documents



To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:





  Copyright (C)  year  your name.
  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.3
  or any later version published by the Free Software Foundation;
  with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
  Texts.  A copy of the license is included in the section entitled ``GNU
  Free Documentation License''.




If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the “with…Texts.” line with this:





    with the Invariant Sections being list their titles, with
    the Front-Cover Texts being list, and with the Back-Cover Texts
    being list.




If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.



If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.










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Footnotes



(1)


A good
introduction to Git is free Pro Git book, which is available online at
https://git-scm.com/book/en/v2






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