  
  [1X76 [33X[0;0YUsing GAP Packages[133X[101X
  
  [33X[0;0YThe  functionality  of  [5XGAP[105X  can  be  extended  by loading [5XGAP[105X packages. [5XGAP[105X
  distribution  already contains all currently redistributed with [5XGAP[105X packages
  in the [11Xgap4r7/pkg[111X directory.[133X
  
  [33X[0;0Y[5XGAP[105X  packages  are written by (groups of) [5XGAP[105X users which may not be members
  of the [5XGAP[105X developer team. The responsibility and copyright of a [5XGAP[105X package
  remains with the original author(s).[133X
  
  [33X[0;0Y[5XGAP[105X  packages have their own documentation which is smoothly integrated into
  the [5XGAP[105X help system.[133X
  
  [33X[0;0YAll [5XGAP[105X users who develop new code are invited to share the results of their
  efforts  with  other  [5XGAP[105X  users  by  making  the code and its documentation
  available in form of a package. Information how to do this is available from
  the [5XGAP[105X Web pages ([7Xhttp://www.gap-system.org[107X) and in the [5XGAP[105X package [5XExample[105X
  (see     [7Xhttp://www.gap-system.org/Packages/example.html[107X).     There     are
  possibilities  to  get  a  package  distributed  together with [5XGAP[105X and it is
  possible to submit a package to a formal refereeing process.[133X
  
  [33X[0;0YIn this chapter we describe how to use existing packages.[133X
  
  
  [1X76.1 [33X[0;0YInstalling a GAP Package[133X[101X
  
  [33X[0;0YBefore  a  package  can  be  used  it  must  be  installed.  With a standard
  installation  of  [5XGAP[105X  there  should be all currently redistributed with [5XGAP[105X
  packages   already   available.   But   since   [5XGAP[105X  packages  are  released
  independently  of  the  main  [5XGAP[105X  system  it  may be sensible to upgrade or
  install new packages between upgrades of your [5XGAP[105X installation.[133X
  
  [33X[0;0YA  package  consists of a collection of files within a single directory that
  must  be  a  subdirectory  of  the  [11Xpkg[111X  directory  in  one  of the [5XGAP[105X root
  directories, see [14X9.2[114X. (If you don't have access to the [11Xpkg[111X directory in your
  main  [5XGAP[105X  installation you can add private root directories as explained in
  that section.)[133X
  
  [33X[0;0YWhenever  you  get  from  somewhere an archive of a [5XGAP[105X package it should be
  accompanied with a [11XREADME[111X file that explains its installation. Some packages
  just  consist  of  [5XGAP[105X  code  and  the installation is done by unpacking the
  archive  in  one of the places described above. There are also packages that
  need  further  installation  steps,  there  may be for example some external
  programs  which  have  to  be  compiled  (this  is often done by just saying
  [10X./configure;  make[110X  inside  the  unpacked  package  directory, but check the
  individual  [11XREADME[111X  files). Note that if you use Windows you may not be able
  to use some or all external binaries.[133X
  
  
  [1X76.2 [33X[0;0YLoading a GAP Package[133X[101X
  
  [33X[0;0YSome  [5XGAP[105X  packages are prepared for [13Xautomatic loading[113X, that is they will be
  loaded automatically with [5XGAP[105X, others must in each case be separately loaded
  by a call to [2XLoadPackage[102X ([14X76.2-1[114X).[133X
  
  [1X76.2-1 LoadPackage[101X
  
  [29X[2XLoadPackage[102X( [3Xname[103X[, [3Xversion[103X][, [3Xbanner[103X] ) [32X function
  
  [33X[0;0Yloads the [5XGAP[105X package with name [3Xname[103X. If the optional version string [3Xversion[103X
  is  given,  the  package will only be loaded in a version number at least as
  large  as  [3Xversion[103X,  or  equal  to  [3Xversion[103X  if  its  first  character  is [10X=[110X
  (see [2XCompareVersionNumbers[102X ([14X76.3-6[114X)). The argument [3Xname[103X is case insensitive.[133X
  
  [33X[0;0Y[2XLoadPackage[102X will return [9Xtrue[109X if the package has been successfully loaded and
  will  return  [9Xfail[109X if the package could not be loaded. The latter may be the
  case  if  the  package is not installed, if necessary binaries have not been
  compiled, or if the version number of the available version is too small. If
  the  package  cannot be loaded, [2XTestPackageAvailability[102X ([14X76.3-2[114X) can be used
  to  find the reasons. Also, [2XDisplayPackageLoadingLog[102X ([14X76.2-4[114X) can be used to
  find  out  more about the failure reasons. To see the problems directly, one
  can  change the verbosity using the user preference [10XInfoPackageLoadingLevel[110X,
  see [2XInfoPackageLoading[102X ([14X76.2-4[114X) for details.[133X
  
  [33X[0;0YIf  the package [3Xname[103X has already been loaded in a version number at least or
  equal  to  [3Xversion[103X,  respectively,  [2XLoadPackage[102X  returns  [9Xtrue[109X without doing
  anything else.[133X
  
  [33X[0;0YThe  argument  [3Xname[103X  may be the prefix of a package name. If no package with
  name  [3Xname[103X  is installed, the behaviour is as follows. If [3Xname[103X is the prefix
  of  exactly one name of an installed package then [2XLoadPackage[102X is called with
  this  name;  if the names of several installed packages start with [3Xname[103X then
  the these names are printed, and [2XLoadPackage[102X returns [9Xfail[109X. Thus the names of
  [13Xall[113X  installed  packages  can  be shown by calling [2XLoadPackage[102X with an empty
  string.[133X
  
  [33X[0;0YIf  the  optional  argument [3Xbanner[103X is present then it must be either [9Xtrue[109X or
  [9Xfalse[109X; in the latter case, the effect is that no package banner is printed.[133X
  
  [33X[0;0YAfter  a  package  has  been  loaded  its  code  and documentation should be
  available as other parts of the [5XGAP[105X library are.[133X
  
  [33X[0;0YWhen  [5XGAP[105X  is started then some packages are loaded automatically. These are
  the packages listed in [10XGAPInfo.Dependencies.NeededOtherPackages[110X and (if this
  is not disabled, see below) [10XUserPreference( "PackagesToLoad" )[110X.[133X
  
  [33X[0;0YA  [5XGAP[105X  package  may  also  install only its documentation automatically but
  still  need  loading  by  [2XLoadPackage[102X.  In  this  situation  the online help
  displays  [10X(not  loaded)[110X in the header lines of the manual pages belonging to
  this [5XGAP[105X package.[133X
  
  [33X[0;0YIf  for  some  reason  you  don't  want certain packages to be automatically
  loaded, [5XGAP[105X provides three levels for disabling autoloading:[133X
  
  [33X[0;0YThe  autoloading  of  specific packages can be overwritten [13Xfor the whole [5XGAP[105X
  installation[113X  by  putting  a  file [11XNOAUTO[111X into a [11Xpkg[111X directory that contains
  lines with the names of packages which should not be automatically loaded.[133X
  
  [33X[0;0YFurthermore,  [13Xindividual  users[113X  can  disable  the  autoloading  of specific
  packages  by  putting  the  names  of  these  packages into the list that is
  assigned  to  the  user  preference  [21XExcludeFromAutoload[121X, for example in the
  user's [11Xgap.ini[111X file (see [14X3.2-1[114X).[133X
  
  [33X[0;0YUsing  the  [10X-A[110X command line option when starting up [5XGAP[105X (see [14X3.1[114X), automatic
  loading of packages is switched off [13Xfor this [5XGAP[105X session[113X.[133X
  
  [33X[0;0YIn    any   of   the   above   three   cases,   the   packages   listed   in
  [10XGAPInfo.Dependencies.NeededOtherPackages[110X are still loaded automatically, and
  an error is signalled if not all of these packages are available.[133X
  
  [33X[0;0YSee  [2XSetPackagePath[102X  ([14X76.2-2[114X)  for  a possibility to force that a prescribed
  package  version will be loaded. See also [2XExtendRootDirectories[102X ([14X76.2-3[114X) for
  a  possibility  to  add  directories  containing packages after [5XGAP[105X has been
  started.[133X
  
  [1X76.2-2 SetPackagePath[101X
  
  [29X[2XSetPackagePath[102X( [3Xpkgname[103X, [3Xpkgpath[103X ) [32X function
  
  [33X[0;0YLet  [3Xpkgname[103X  and  [3Xpkgpath[103X be strings denoting the name of a [5XGAP[105X package and
  the path to a directory where a version of this package can be found (i. e.,
  calling  [2XDirectory[102X  ([14X9.3-2[114X) with the argument [3Xpkgpath[103X will yield a directory
  that contains the file [11XPackageInfo.g[111X of the package).[133X
  
  [33X[0;0YIf the package [3Xpkgname[103X is already loaded with an installation path different
  from [3Xpkgpath[103X then [2XSetPackagePath[102X signals an error. If the package [3Xpkgname[103X is
  not  yet  loaded  then [2XSetPackagePath[102X erases the information about available
  versions  of the package [3Xpkgname[103X, and stores the record that is contained in
  the  [11XPackageInfo.g[111X  file  at  [3Xpkgpath[103X  instead,  such  that only the version
  installed at [3Xpkgpath[103X can be loaded with [2XLoadPackage[102X ([14X76.2-1[114X).[133X
  
  [33X[0;0YThis  function  can  be  used to force [5XGAP[105X to load a particular version of a
  package, although newer versions of the package might be available.[133X
  
  [1X76.2-3 ExtendRootDirectories[101X
  
  [29X[2XExtendRootDirectories[102X( [3Xpaths[103X ) [32X function
  
  [33X[0;0YLet  [3Xpaths[103X  be  a  list  of  strings  that denote paths to intended [5XGAP[105X root
  directories  (see  [14X9.2[114X). The function [2XExtendRootDirectories[102X adds these paths
  to  the  global  list  [10XGAPInfo.RootPaths[110X  and  calls  the  initialization of
  available  [5XGAP[105X  packages, such that later calls to [2XLoadPackage[102X ([14X76.2-1[114X) will
  find  the  [5XGAP[105X  packages  that  are  contained  in [11Xpkg[111X subdirectories of the
  directories given by [3Xpaths[103X.[133X
  
  [33X[0;0YNote  that the purpose of this function is to make [5XGAP[105X packages in the given
  directories  available.  It  cannot  be  used to influence the start of [5XGAP[105X,
  because the [5XGAP[105X library is loaded before [2XExtendRootDirectories[102X can be called
  (and because [10XGAPInfo.RootPaths[110X is not used for reading the [5XGAP[105X library).[133X
  
  [1X76.2-4 DisplayPackageLoadingLog[101X
  
  [29X[2XDisplayPackageLoadingLog[102X( [[3Xseverity[103X] ) [32X function
  [29X[2XInfoPackageLoading[102X[32X info class
  [29X[2XPACKAGE_ERROR[102X[32X global variable
  [29X[2XPACKAGE_WARNING[102X[32X global variable
  [29X[2XPACKAGE_INFO[102X[32X global variable
  [29X[2XPACKAGE_DEBUG[102X[32X global variable
  [29X[2XLogPackageLoadingMessage[102X( [3Xseverity[103X, [3Xmessage[103X[, [3Xname[103X] ) [32X function
  
  [33X[0;0YWhenever  [5XGAP[105X  considers  loading a package, log messages are collected in a
  global  list. The messages for the current [5XGAP[105X session can be displayed with
  [2XDisplayPackageLoadingLog[102X.  To each message, a [21Xseverity[121X is assigned, which is
  one  of  [2XPACKAGE_ERROR[102X,  [2XPACKAGE_WARNING[102X,  [2XPACKAGE_INFO[102X,  [2XPACKAGE_DEBUG[102X,  in
  increasing  order.  The  function  [2XDisplayPackageLoadingLog[102X  shows  only the
  messages  whose  severity  is  at most [3Xseverity[103X, the default for [3Xseverity[103X is
  [2XPACKAGE_WARNING[102X.[133X
  
  [33X[0;0YThe intended meaning of the severity levels is as follows.[133X
  
  [8XPACKAGE_ERROR[108X
        [33X[0;6Yshould  be  used  whenever  [5XGAP[105X  will run into an error during package
        loading,  where  the  reason  of  the error shall be documented in the
        global list.[133X
  
  [8XPACKAGE_WARNING[108X
        [33X[0;6Yshould be used whenever [5XGAP[105X has detected a reason why a package cannot
        be  loaded, and where the message describes how to solve this problem,
        for example if a package binary is missing.[133X
  
  [8XPACKAGE_INFO[108X
        [33X[0;6Yshould be used whenever [5XGAP[105X has detected a reason why a package cannot
        be  loaded,  and  where it is not clear how to solve this problem, for
        example  if  the  package  is  not  compatible  with  other  installed
        packages.[133X
  
  [8XPACKAGE_DEBUG[108X
        [33X[0;6Yshould  be  used  for  other  messages reporting what [5XGAP[105X does when it
        loads  packages  (checking  dependencies,  reading  files,  etc.). One
        purpose  is to record in which order packages have been considered for
        loading or have actually been loaded.[133X
  
  [33X[0;0YThe  log  messages  are  created  either  by  the functions of [5XGAP[105X's package
  loading  mechanism  or  in  the  code  of  your  package, for example in the
  [10XAvailabilityTest[110X function of the package's [11XPackageInfo.g[111X file (see [14X76.3-11[114X),
  using  [2XLogPackageLoadingMessage[102X. The arguments of this function are [3Xseverity[103X
  (which  must  be  one  of the above severity levels), [3Xmessage[103X (which must be
  either  a  string  or a list of strings), and optionally [3Xname[103X (which must be
  the  name of the package to which the message belongs). The argument [3Xname[103X is
  not   needed  if  the  function  is  called  from  a  call  of  a  package's
  [10XAvailabilityTest[110X  function  (see  [14X76.3-11[114X)  or is called from a package file
  that  is read from [11Xinit.g[111X or [11Xread.g[111X; in these cases, the name of the current
  package (stored in the record [10XGAPInfo.PackageCurrent[110X) is taken. According to
  the above list, the [3Xseverity[103X argument of [2XLogPackageLoadingMessage[102X calls in a
  package's   [10XAvailabilityTest[110X   function   is   either   [2XPACKAGE_WARNING[102X   or
  [2XPACKAGE_INFO[102X.[133X
  
  [33X[0;0YIf  you  want  to  see  the  log messages already during the package loading
  process,  you  can set the level of the info class [2XInfoPackageLoading[102X to one
  of  the  severity  values listed above; afterwards the messages with at most
  this  severity  are shown immediately when they arise. In order to make this
  work     already     for     autoloaded     packages,     you    can    call
  [10XSetUserPreference("InfoPackageLoadingLevel",   [3Xlev[103X[10X);[110X   to  set  the  desired
  severity  level  [3Xlev[103X. This can for example be done in your [11Xgap.ini[111X file, see
  Section [14X3.2-1[114X.[133X
  
  
  [1X76.3 [33X[0;0YFunctions for GAP Packages[133X[101X
  
  [33X[0;0YThe  following functions are mainly used in files contained in a package and
  not by users of a package.[133X
  
  [1X76.3-1 ReadPackage[101X
  
  [29X[2XReadPackage[102X( [[3Xname[103X, ][3Xfile[103X ) [32X function
  [29X[2XRereadPackage[102X( [[3Xname[103X, ][3Xfile[103X ) [32X function
  
  [33X[0;0YCalled  with  two  strings [3Xname[103X and [3Xfile[103X, [2XReadPackage[102X reads the file [3Xfile[103X of
  the  [5XGAP[105X  package  [3Xname[103X,  where [3Xfile[103X is given as a path relative to the home
  directory  of  [3Xname[103X. Note that [3Xfile[103X is read in the namespace of the package,
  see Section [14X4.10[114X for details.[133X
  
  [33X[0;0YIf  only  one  argument  [3Xfile[103X  is  given,  this should be the path of a file
  relative  to  the [11Xpkg[111X subdirectory of [5XGAP[105X root paths (see [14X9.2[114X). Note that in
  this  case,  the  package  name  is assumed to be equal to the first part of
  [3Xfile[103X, [13Xso the one argument form is not recommended[113X.[133X
  
  [33X[0;0YThe  absolute  path is determined as follows. If the package in question has
  already  been loaded then the file in the directory of the loaded version is
  read.  If  the  package  is  available but not yet loaded then the directory
  given  by  [2XTestPackageAvailability[102X  ([14X76.3-2[114X)  is  used,  without  prescribed
  version  number.  (Note that the [2XReadPackage[102X call does [13Xnot[113X force the package
  to be loaded.)[133X
  
  [33X[0;0YIf the file is readable then [9Xtrue[109X is returned, otherwise [9Xfalse[109X.[133X
  
  [33X[0;0YEach  of  [3Xname[103X  and  [3Xfile[103X  should  be  a  string.  The [3Xname[103X argument is case
  insensitive.[133X
  
  [33X[0;0Y[2XRereadPackage[102X  does  the  same  as  [2XReadPackage[102X,  except that also read-only
  global variables are overwritten (cf. [2XReread[102X ([14X9.7-9[114X)).[133X
  
  [1X76.3-2 TestPackageAvailability[101X
  
  [29X[2XTestPackageAvailability[102X( [3Xname[103X[, [3Xversion[103X][, [3Xcheckall[103X] ) [32X function
  
  [33X[0;0YFor  strings  [3Xname[103X  and [3Xversion[103X, this function tests whether the [5XGAP[105X package
  [3Xname[103X  is  available  for  loading  in a version that is at least [3Xversion[103X, or
  equal   to   [3Xversion[103X   if   the   first  character  of  [3Xversion[103X  is  [10X=[110X  (see
  [2XCompareVersionNumbers[102X ([14X76.3-6[114X) for further details about version numbers).[133X
  
  [33X[0;0YThe  result  is  [9Xtrue[109X  if  the  package is already loaded, [9Xfail[109X if it is not
  available,  and  the  string  denoting  the  [5XGAP[105X root path where the package
  resides  if  it  is  available,  but  not yet loaded. So the package [3Xname[103X is
  available if the result of [2XTestPackageAvailability[102X is not equal to [9Xfail[109X.[133X
  
  [33X[0;0YIf the optional argument [3Xcheckall[103X is [9Xtrue[109X then all dependencies are checked,
  even if some have turned out to be not satisfied. This is useful when one is
  interested  in  the  reasons  why the package [3Xname[103X cannot be loaded. In this
  situation,     calling     first     [2XTestPackageAvailability[102X     and    then
  [2XDisplayPackageLoadingLog[102X  ([14X76.2-4[114X)  with argument [2XPACKAGE_INFO[102X ([14X76.2-4[114X) will
  give an overview of these reasons.[133X
  
  [33X[0;0YYou  should  [13Xnot[113X  call  [2XTestPackageAvailability[102X  in  the  test function of a
  package  (the  value  of the component [10XAvailabilityTest[110X in the [11XPackageInfo.g[111X
  file  of  the  package,  see [14X76.3-11[114X), because [2XTestPackageAvailability[102X calls
  this test function.[133X
  
  [33X[0;0YThe argument [3Xname[103X is case insensitive.[133X
  
  [1X76.3-3 InstalledPackageVersion[101X
  
  [29X[2XInstalledPackageVersion[102X( [3Xname[103X ) [32X function
  
  [33X[0;0YIf   the   [5XGAP[105X   package  with  name  [3Xname[103X  has  already  been  loaded  then
  [2XInstalledPackageVersion[102X  returns  the  string denoting the version number of
  this  version  of  the  package. If the package is available but has not yet
  been  loaded  then the version number string for that version of the package
  that  currently  would  be  loaded. (Note that loading [13Xanother[113X package might
  force  loading  another  version  of  the  package  [3Xname[103X,  so  the result of
  [2XInstalledPackageVersion[102X will be different afterwards.) If the package is not
  available then [9Xfail[109X is returned.[133X
  
  [33X[0;0YThe argument [3Xname[103X is case insensitive.[133X
  
  [1X76.3-4 DirectoriesPackageLibrary[101X
  
  [29X[2XDirectoriesPackageLibrary[102X( [3Xname[103X[, [3Xpath[103X] ) [32X function
  
  [33X[0;0Ytakes  the  string  [3Xname[103X,  a  name  of  a [5XGAP[105X package, and returns a list of
  directory   objects  for  those  sub-directory/ies  containing  the  library
  functions  of this [5XGAP[105X package, for the version that is already loaded or is
  currently  going to be loaded or would be the first version [5XGAP[105X would try to
  load  if  no other version is explicitly prescribed. (If the package [3Xname[103X is
  not yet loaded then we cannot guarantee that the returned directories belong
  to a version that really can be loaded.)[133X
  
  [33X[0;0YThe default is that the library functions are in the subdirectory [11Xlib[111X of the
  [5XGAP[105X  package's  home  directory.  If  this  is not the case, then the second
  argument  [3Xpath[103X  needs to be present and must be a string that is a path name
  relative to the home directory of the [5XGAP[105X package with name [3Xname[103X.[133X
  
  [33X[0;0YNote   that   [2XDirectoriesPackageLibrary[102X  is  likely  to  be  called  in  the
  [10XAvailabilityTest[110X function in the package's [11XPackageInfo.g[111X file (see [14X76.3-11[114X).[133X
  
  [33X[0;0YAs  an  example,  the  following  returns a directory object for the library
  functions of the [5XGAP[105X package [5XExample[105X:[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XDirectoriesPackageLibrary( "Example", "gap" );[127X[104X
    [4X[28X[ dir("/home/werner/gap/4.0/pkg/example/gap/") ][128X[104X
  [4X[32X[104X
  
  [33X[0;0YObserve  that  we  needed  the  second  argument [10X"gap"[110X here, since [5XExample[105X's
  library functions are in the subdirectory [11Xgap[111X rather than [11Xlib[111X.[133X
  
  [33X[0;0YIn  order  to  find  a  subdirectory  deeper  than  one  level  in a package
  directory, the second argument is again necessary whether or not the desired
  subdirectory  relative  to  the  package's  directory  begins  with [11Xlib[111X. The
  directories in [3Xpath[103X should be separated by [10X/[110X (even on systems, like Windows,
  which  use  [10X\[110X  as  the directory separator). For example, suppose there is a
  package  [10Xsomepackage[110X  with a subdirectory [11Xm11[111X in the directory [11Xdata[111X, then we
  might expect the following:[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XDirectoriesPackageLibrary( "somepackage", "data/m11" );[127X[104X
    [4X[28X[ dir("/home/werner/gap/4.0/pkg/somepackage/data/m11") ][128X[104X
  [4X[32X[104X
  
  [1X76.3-5 DirectoriesPackagePrograms[101X
  
  [29X[2XDirectoriesPackagePrograms[102X( [3Xname[103X ) [32X function
  
  [33X[0;0Yreturns  a  list of the [10Xbin/[110X[3Xarchitecture[103X subdirectories of all packages [3Xname[103X
  where  [3Xarchitecture[103X is the architecture on which [5XGAP[105X has been compiled (this
  can  be  accessed  as  [10XGAPInfo.Architecture[110X,  see  [2XGAPInfo[102X  ([14X3.5-1[114X)) and the
  version  of  the installed package coincides with the version of the package
  [3Xname[103X  that  is already loaded or is currently going to be loaded or would be
  the  first  version  [5XGAP[105X would try to load if no other version is explicitly
  prescribed.  (If the package [3Xname[103X is not yet loaded then we cannot guarantee
  that  the  returned  directories  belong  to  a  version  that really can be
  loaded.)[133X
  
  [33X[0;0YNote   that  [2XDirectoriesPackagePrograms[102X  is  likely  to  be  called  in  the
  [10XAvailabilityTest[110X function in the package's [11XPackageInfo.g[111X file (see [14X76.3-11[114X).[133X
  
  [33X[0;0YThe  directories  returned by [2XDirectoriesPackagePrograms[102X are the place where
  external  binaries  of  the [5XGAP[105X package [3Xname[103X for the current package version
  and the current architecture should be located.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XDirectoriesPackagePrograms( "nq" );[127X[104X
    [4X[28X[ dir("/home/gap/4.0/pkg/nq/bin/x86_64-unknown-linux-gnu-gcc/64-bit/"),[128X[104X
    [4X[28X  dir("/home/gap/4.0/pkg/nq/bin/x86_64-unknown-linux-gnu-gcc/") ][128X[104X
  [4X[32X[104X
  
  [1X76.3-6 CompareVersionNumbers[101X
  
  [29X[2XCompareVersionNumbers[102X( [3Xsupplied[103X, [3Xrequired[103X[, [3X"equal"[103X] ) [32X function
  
  [33X[0;0YA  version  number is a string which contains nonnegative integers separated
  by  non-numeric  characters.  Examples  of  valid  version  numbers  are for
  example:[133X
  
  [4X[32X  Example  [32X[104X
    [4X[28X"1.0"   "3.141.59"  "2-7-8.3" "5 release 2 patchlevel 666"[128X[104X
  [4X[32X[104X
  
  [33X[0;0Y[2XCompareVersionNumbers[102X  compares  two version numbers, given as strings. They
  are  split at non-digit characters, the resulting integer lists are compared
  lexicographically.  The  routine tests whether [3Xsupplied[103X is at least as large
  as  [3Xrequired[103X, and returns [9Xtrue[109X or [9Xfalse[109X accordingly. A version number ending
  in [10Xdev[110X is considered to be infinite.[133X
  
  [1X76.3-7 IsPackageMarkedForLoading[101X
  
  [29X[2XIsPackageMarkedForLoading[102X( [3Xname[103X, [3Xversion[103X ) [32X function
  
  [33X[0;0YThis  function  can  be  used  in  the code of a package [22XA[122X, say, for testing
  whether  the  package  [3Xname[103X  in  version  [3Xversion[103X  will  be loaded after the
  [2XLoadPackage[102X  ([14X76.2-1[114X)  call  for the package [22XA[122X has been executed. This means
  that  the  package  [3Xname[103X  had  been  loaded before, or has been (directly or
  indirectly)  requested  as a needed or suggested package of the package [22XA[122X or
  of a package whose loading requested that [22XA[122X was loaded.[133X
  
  [1X76.3-8 DeclareAutoreadableVariables[101X
  
  [29X[2XDeclareAutoreadableVariables[102X( [3Xpkgname[103X, [3Xfilename[103X, [3Xvarlist[103X ) [32X function
  
  [33X[0;0YLet  [3Xpkgname[103X  be  the  name of a package, let [3Xfilename[103X be the name of a file
  relative to the home directory of this package, and let [3Xvarlist[103X be a list of
  strings that are the names of global variables which get bound when the file
  is  read.  [2XDeclareAutoreadableVariables[102X  notifies  the names in [3Xvarlist[103X such
  that  the first attempt to access one of the variables causes the file to be
  read.[133X
  
  
  [1X76.3-9 [33X[0;0YKernel modules in [5XGAP[105X[101X[1X packages[133X[101X
  
  [33X[0;0YIf  the  package  has a kernel module, then it can be compiled using the [5Xgac[105X
  script.  A kernel module is implemented in C and follows certain conventions
  to comply with the [5XGAP[105X kernel interface, which we plan to document later. In
  the  meantime,  we advice to get in touch with [5XGAP[105X developers if you plan to
  develop such a package.[133X
  
  [33X[0;0YTo  use the [5Xgac[105X script to produce dynamically loadable modules, call it with
  the [10X-d[110X option, for example:[133X
  
  [4X[32X  Example  [32X[104X
    [4X[28X$ gap4/bin/i386-ibm-linux-gcc2/gac -d test.c[128X[104X
  [4X[32X[104X
  
  [33X[0;0YThis  will  produce  a  file [11Xtest.so[111X, which then can be loaded into [5XGAP[105X with
  [2XLoadDynamicModule[102X ([14X76.3-10[114X).[133X
  
  [1X76.3-10 LoadDynamicModule[101X
  
  [29X[2XLoadDynamicModule[102X( [3Xfilename[103X[, [3Xcrc[103X] ) [32X function
  
  [33X[0;0YTo load a compiled file, the command [2XLoadDynamicModule[102X is used. This command
  loads  [3Xfilename[103X  as  module.  If  given, the CRC checksum [3Xcrc[103X must match the
  value of the module (see [14X9.7-7[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XLoadDynamicModule("./test.so");[127X[104X
    [4X[25Xgap>[125X [27XCrcFile("test.so");[127X[104X
    [4X[28X2906458206[128X[104X
    [4X[25Xgap>[125X [27XLoadDynamicModule("./test.so",1);[127X[104X
    [4X[28XError, <crc> mismatch (or no support for dynamic loading) called from[128X[104X
    [4X[28X<function>( <arguments> ) called from read-eval-loop[128X[104X
    [4X[28XEntering break read-eval-print loop ...[128X[104X
    [4X[28Xyou can 'quit;' to quit to outer loop, or[128X[104X
    [4X[28Xyou can 'return;' to continue[128X[104X
    [4X[26Xbrk>[126X [27Xquit;[127X[104X
    [4X[25Xgap>[125X [27XLoadDynamicModule("./test.so",2906458206);[127X[104X
  [4X[32X[104X
  
  [33X[0;0YOn  some  operating  systems,  once  you have loaded a dynamic module with a
  certain  filename,  loading  another  with  the  same  filename will have no
  effect, even if the file on disk has changed.[133X
  
  
  [1X76.3-11 [33X[0;0YThe PackageInfo.g File[133X[101X
  
  [33X[0;0YEach  package  has  the  file  [11XPackageInfo.g[111X which contains meta-information
  about  the  package  (package  name,  version, author(s), relations to other
  packages,  homepage,  download archives, banner, etc.). This file is used by
  the  package loading mechanism and also for the distribution of a package to
  other users.[133X
  
  [1X76.3-12 ValidatePackageInfo[101X
  
  [29X[2XValidatePackageInfo[102X( [3Xinfo[103X ) [32X function
  
  [33X[0;0YThis  function  is  intended to support package authors who create or modify
  [11XPackageInfo.g[111X  files. (It is [13Xnot[113X called when these files are read during the
  startup of [5XGAP[105X or when packages are actually loaded.)[133X
  
  [33X[0;0YThe argument [3Xinfo[103X must be either a record as is contained in a [11XPackageInfo.g[111X
  file  or  a  a string which describes the path to such a file. The result is
  [9Xtrue[109X  if  the  record or the contents of the file, respectively, has correct
  format,  and  [9Xfalse[109X  otherwise;  in  the  latter  case information about the
  incorrect components is printed.[133X
  
  [33X[0;0YNote that the components used for package loading are checked as well as the
  components  that  are  needed for composing the package overview web page or
  for updating the package archives.[133X
  
  [33X[0;0YIf  [3Xinfo[103X  is  a  string then [2XValidatePackageInfo[102X checks additionally whether
  those  package  files exist that are mentioned in the file [11Xinfo[111X, for example
  the [11Xmanual.six[111X file of the package documentation.[133X
  
  [1X76.3-13 ShowPackageVariables[101X
  
  [29X[2XShowPackageVariables[102X( [3Xpkgname[103X[, [3Xversion[103X][, [3Xarec[103X] ) [32X function
  [29X[2XPackageVariablesInfo[102X( [3Xpkgname[103X, [3Xversion[103X ) [32X function
  
  [33X[0;0YLet  [3Xpkgname[103X  be  the  name  of  a  [5XGAP[105X  package.  If the package [3Xpkgname[103X is
  available  but  not  yet  loaded  then [2XShowPackageVariables[102X prints a list of
  global variables that become bound and of methods that become installed when
  the package is loaded. (For that, [5XGAP[105X actually loads the package.)[133X
  
  [33X[0;0YIf  a  version  number  [3Xversion[103X  is  given  (see  Section [14X'Example:  Version
  Numbers'[114X) then this version of the package is considered.[133X
  
  [33X[0;0YAn  error  message  is  printed if (the given version of) the package is not
  available or already loaded.[133X
  
  [33X[0;0YInformation  is printed about new and redeclared global variables, and about
  names  of  global  variables  introduced  in  the  package  that differ from
  existing  globals  only  by  case;  note  that  the  [5XGAP[105X help system is case
  insensitive,  so it is difficult to document identifiers that differ only by
  case.[133X
  
  [33X[0;0YInfo lines for undocumented variables are marked with an asterisk [10X*[110X.[133X
  
  [33X[0;0YThe  following entries are omitted from the list: default setter methods for
  attributes  and properties that are declared in the package, and [10XSet[3Xattr[103X[10X[110X and
  [10XHas[3Xattr[103X[10X[110X type variables where [3Xattr[103X is an attribute or property.[133X
  
  [33X[0;0YThe  output  can be customized using the optional record [3Xarec[103X, the following
  components of this record are supported.[133X
  
  [8X[10Xshow[110X[108X
        [33X[0;6Ya  list  of strings describing those kinds of variables which shall be
        shown,  such as [10X"new global functions"[110X; the default are all kinds that
        appear in the package,[133X
  
  [8X[10XshowDocumented[110X[108X
        [33X[0;6Y[9Xtrue[109X  (the  default) if documented variables shall be shown, and [9Xfalse[109X
        otherwise,[133X
  
  [8X[10XshowUndocumented[110X[108X
        [33X[0;6Y[9Xtrue[109X (the default) if undocumented variables shall be shown, and [9Xfalse[109X
        otherwise,[133X
  
  [8X[10XshowPrivate[110X[108X
        [33X[0;6Y[9Xtrue[109X  (the  default)  if  variables from the package's name space (see
        Section [14X4.10[114X) shall be shown, and [9Xfalse[109X otherwise,[133X
  
  [8X[10XDisplay[110X[108X
        [33X[0;6Ya function that takes a string and shows it on the screen; the default
        is [2XPrint[102X ([14X6.3-4[114X), another useful value is [2XPager[102X ([14X2.4-1[114X).[133X
  
  [33X[0;0YAn   interactive   variant   of   [2XShowPackageVariables[102X   is   the   function
  [2XBrowsePackageVariables[102X  ([14XBrowse: BrowsePackageVariables[114X) that is provided by
  the [5XGAP[105X package [5XBrowse[105X. For this function, it is not sensible to assume that
  the  package [3Xpkgname[103X is not yet loaded before the function call, because one
  might be interested in packages that must be loaded before [5XBrowse[105X itself can
  be   loaded.   The   solution   is   that   [2XBrowsePackageVariables[102X  ([14XBrowse:
  BrowsePackageVariables[114X)  takes  the  output  of  [2XPackageVariablesInfo[102X as its
  second   argument.   The  function  [2XPackageVariablesInfo[102X  is  used  by  both
  [2XShowPackageVariables[102X        and        [2XBrowsePackageVariables[102X       ([14XBrowse:
  BrowsePackageVariables[114X)  for collecting the information about the package in
  question, and can be called before the package [5XBrowse[105X is loaded.[133X
  
  [1X76.3-14 BibEntry[101X
  
  [29X[2XBibEntry[102X( [3Xpkgname[103X[, [3Xkey[103X] ) [32X function
  [6XReturns:[106X  [33X[0;10Ya  string in BibXMLext format (see [14X'GAPDoc: The BibXMLext Format'[114X)
            that can be used for referencing the [5XGAP[105X system or a [5XGAP[105X package.[133X
  
  [33X[0;0YIf  the  argument [3Xpkgname[103X is the string [10X"GAP"[110X, the function returns an entry
  for the current version of [5XGAP[105X.[133X
  
  [33X[0;0YOtherwise, if a string [3Xpkgname[103X is given, which is the name of a [5XGAP[105X package,
  an  entry  for  this  package  is  returned; this entry is computed from the
  [11XPackageInfo.g[111X   file   of   [13Xthe   current   version[113X   of  the  package,  see
  [2XInstalledPackageVersion[102X  ([14X76.3-3[114X).  If  no  package  with  name  [3Xpkgname[103X  is
  installed then the empty string is returned.[133X
  
  [33X[0;0YA  string  for  [13Xa  different  version[113X of [5XGAP[105X or a package can be computed by
  entering, as the argument [3Xpkgname[103X, the desired record from the [11XPackageInfo.g[111X
  file. (One can access these records using the function [10XPackageInfo[110X.)[133X
  
  [33X[0;0YIn  each of the above cases, an optional argument [3Xkey[103X can be given, a string
  which is then used as the key of the BibTeX entry instead of the default key
  that is generated from the system/package name and the version number.[133X
  
  [33X[0;0Y[2XBibEntry[102X  requires  the  functions [2XFormatParagraph[102X ([14XGAPDoc: FormatParagraph[114X)
  and [2XNormalizedNameAndKey[102X ([14XGAPDoc: NormalizedNameAndKey[114X) from the [5XGAP[105X package
  [5XGAPDoc[105X.[133X
  
  [33X[0;0YThe   functions   [2XParseBibXMLextString[102X  ([14XGAPDoc:  ParseBibXMLextString[114X)  and
  [2XStringBibXMLEntry[102X  ([14XGAPDoc:  StringBibXMLEntry[114X)  can  be  used to create for
  example a BibTeX entry from the return value, as follows.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xbib:= BibEntry( "GAP", "GAP4.5" );;[127X[104X
    [4X[25Xgap>[125X [27XPrint( bib, "\n" );[127X[104X
    [4X[28X<entry id="GAP4.5"><misc>[128X[104X
    [4X[28X  <title><C>GAP</C> &ndash; <C>G</C>roups, <C>A</C>lgorithms,[128X[104X
    [4X[28X         and <C>P</C>rogramming, <C>V</C>ersion 4.5.1</title>[128X[104X
    [4X[28X  <howpublished><URL>http://www.gap-system.org</URL></howpublished>[128X[104X
    [4X[28X  <key>GAP</key>[128X[104X
    [4X[28X  <keywords>groups; *; gap; manual</keywords>[128X[104X
    [4X[28X  <other type="organization">The GAP <C>G</C>roup</other>[128X[104X
    [4X[28X</misc></entry>[128X[104X
    [4X[25Xgap>[125X [27Xparse:= ParseBibXMLextString( bib );;[127X[104X
    [4X[25Xgap>[125X [27XPrint( StringBibXMLEntry( parse.entries[1], "BibTeX" ) );[127X[104X
    [4X[28X@misc{ GAP4.5,[128X[104X
    [4X[28X  title =            {{GAP}   {\textendash}   {G}roups,   {A}lgorithms,  and[128X[104X
    [4X[28X                      {P}rogramming, {V}ersion 4.5.1},[128X[104X
    [4X[28X  organization =     {The GAP {G}roup},[128X[104X
    [4X[28X  howpublished =     {\href                      {http://www.gap-system.org}[128X[104X
    [4X[28X                      {\texttt{http://www.gap-system.org}}},[128X[104X
    [4X[28X  key =              {GAP},[128X[104X
    [4X[28X  keywords =         {groups; *; gap; manual}[128X[104X
    [4X[28X}[128X[104X
  [4X[32X[104X
  
  [1X76.3-15 Cite[101X
  
  [29X[2XCite[102X( [[3Xpkgname[103X[, [3Xkey[103X]] ) [32X function
  
  [33X[0;0YUsed  with  no  arguments  or  with  argument [10X"GAP"[110X (case-insensitive), [2XCite[102X
  displays  instructions  on  citing  the  version  of [5XGAP[105X that is being used.
  Suggestions  are  given  in plain text, HTML, BibXML and BibTeX formats. The
  same  instructions  are  also contained in the [11XCITATION[111X file in the [5XGAP[105X root
  directory.[133X
  
  [33X[0;0YIf [3Xpkgname[103X is the name of a [5XGAP[105X package, instructions on citing this package
  will  be displayed. They will be produced from the [11XPackageInfo.g[111X file of the
  working  version  of  this  package  that  must  be  available  in  the  [5XGAP[105X
  installation  being  used. Otherwise, one will get a warning that no working
  version of the package is available.[133X
  
  [33X[0;0YThe optional 2nd argument [3Xkey[103X has the same meaning as in [2XBibEntry[102X ([14X76.3-14[114X).[133X
  
