%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %W infra.tex ANUPQ documentation - infrastructure Werner Nickel %W Greg Gamble %% %H $Id: infra.tex,v 1.51 2006/01/24 04:57:16 gap Exp $ %% %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Chapter{Infrastructure} Most of the details in this chapter are of a technical nature; the user need only skim over this chapter on a first reading. Mostly, it is enough to know that \beginlist%unordered \item{$\bullet$} you must do a `LoadPackage("anupq");' before you can expect to use a command defined by the {\ANUPQ} package (details are in Section~"Loading the ANUPQ Package"); \item{$\bullet$} partial results of {\ANUPQ} commands and some other data are stored in the `ANUPQData' global variable (details are in Section~"The ANUPQData Record"); \item{$\bullet$} doing `SetInfoLevel(InfoANUPQ, <n>);' for <n> greater than the default value 1 will give progressively more information of what is going on ``behind the scenes'' (details are in Section~"Setting the Verbosity of ANUPQ via Info and InfoANUPQ"); \item{$\bullet$} in Section~"Utility functions" we describe some utility functions and functions that run examples from the collection of examples of this package; \item{$\bullet$} in Section~"Attributes and a Property for fp and pc p-groups" we describe the attributes and property `NuclearRank', `MultiplicatorRank' and `IsCapable'; and \item{$\bullet$} in Section~"Hints and Warnings regarding the use of Options" we describe some troubleshooting strategies. Also this section describes how setting `ANUPQWarnOfOtherOptions := true;' may be useful (particularly for novice users) for detecting misspelt options and diagnosing other option usage problems. \endlist %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{Loading the ANUPQ Package} \index{banner} To use the {\ANUPQ} package, as with any {\GAP} package, it must be requested explicitly. This is done by calling \beginexample gap> LoadPackage( "anupq" ); ------------------------------------------------------------- Loading ANUPQ 3.0 (ANU p-Quotient package) C code by Eamonn O'Brien <obrien@math.auckland.ac.nz> (ANU pq binary version: 1.8) GAP code by Werner Nickel <nickel@mathematik.tu-darmstadt.de> and Greg Gamble <gregg@math.rwth-aachen.de> For help, type: ?ANUPQ ------------------------------------------------------------- true \endexample \index{banner!suppression} In version 2.2 of the {\ANUPQ} package there was an option `pkgbanner' that allowed the user some control on how the banner above was displayed. This only worked with {\GAP}~4.3. Since, the {\ANUPQ} package now requires at least {\GAP}~4.4, this option has been removed. If you still have {\GAP}~4.3 (at least fix4), you will need to use {\ANUPQ}~2.2. Note that since the {\ANUPQ} package uses the `AutomorphimGroupPGroup' function of the {\AutPGrp} package and, in any case, often needs other {\AutPGrp} functions when computing descendants, the user must ensure that the {\AutPGrp} package is also installed, at least version 1.2. If the {\AutPGrp} package is not installed, the {\ANUPQ} package will `fail' to load. Also, if {\GAP} cannot find a working `pq' binary, the call to `LoadPackage' will return `fail'. If you want to load the {\ANUPQ} package by default, you can put the `LoadPackage' command into your `.gaprc' file (see Section~"ref:The .gaprc file" in the {\GAP} Reference Manual). By the way, the novice user of the {\ANUPQ} package should probably also append the line \begintt ANUPQWarnOfOtherOptions := true; \endtt to their `.gaprc' file, somewhere after the `LoadPackage( "anupq" );' command (see~"ANUPQWarnOfOtherOptions"). %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{The ANUPQData Record} This section contains fairly technical details which may be skipped on an initial reading. \>`ANUPQData' V is a {\GAP} record in which the essential data for an {\ANUPQ} session within {\GAP} is stored; its fields are: \beginitems \quad`binary' & the path of the `pq' binary; \quad`tmpdir' & the path of the temporary directory used by the `pq' binary and {\GAP} (i.e.~the directory in which all the `pq''s temporary files are created) (also see "ANUPQDirectoryTemporary" below); \quad`outfile'& the full path of the default `pq' output file; \quad`SPimages'& the full path of the file `GAP_library' to which the `pq' program writes its Standard Presentation images; \quad`version'& the version of the current `pq' binary; \quad`ni' & a data record used by non-interactive functions (see below and Chapter~"Non-interactive ANUPQ Functions"); \quad`io' & list of data records for `PqStart' (see below and~"PqStart") processes; \quad`topqlogfile' & name of file logged to by `ToPQLog' (see~"ToPQLog"); and \quad`logstream' & stream of file logged to by `ToPQLog' (see~"ToPQLog"). \enditems Each time an interactive {\ANUPQ} process is initiated via `PqStart' (see~"PqStart"), an identifying number <ioIndex> is generated for the interactive process and a record `ANUPQData.io[<ioIndex>]' with some or all of the fields listed below is created. Whenever a non-interactive function is called (see Chapter~"Non-interactive ANUPQ Functions"), the record `ANUPQData.ni' is updated with fields that, if bound, have exactly the same purpose as for a `ANUPQData.io[<ioIndex>]' record. \beginitems \quad`stream'& the IOStream opened for interactive {\ANUPQ} process <ioIndex> or non-interactive {\ANUPQ} function; \quad`group'& the group given as first argument to `PqStart', `Pq', `PqEpimorphism', `PqDescendants' or `PqStandardPresentation' (or any synonymous methods); \quad`haspcp'& is bound and set to `true' when a pc presentation is first set inside the `pq' program (e.g.~by `PqPcPresentation' or `PqRestorePcPresentation' or a higher order function like `Pq', `PqEpimorphism', `PqPCover', `PqDescendants' or `PqStandardPresentation' that does a `PqPcPresentation' operation, but *not* `PqStart' which only starts up an interactive {\ANUPQ} process); \quad`gens'& a list of the generators of the group `group' as strings (the same as those passed to the `pq' program); \quad`rels'& a list of the relators of the group `group' as strings (the same as those passed to the `pq' program); \quad`name'& the name of the group whose pc presentation is defined by a call to the `pq' program (according to the `pq' program -- unless you have used the `GroupName' option (see e.g.~"Pq") or applied the function `SetName' (see~"ref:SetName") to the group, the ``generic'' name `"[grp]"' is set as a default); \quad`gpnum'& if not a null string, the ``number'' (i.e.~the unique label assigned by the `pq' program) of the last descendant processed; \quad`class'& the largest lower exponent-$p$ central class of a quotient group of the group (usually `group') found by a call to the `pq' program; \quad`forder'& the factored order of the quotient group of largest lower exponent-$p$ central class found for the group (usually `group') by a call to the `pq' program (this factored order is given as a list `[$p$, $n$]', indicating an order of $p^n$); \quad`pcoverclass'& the lower exponent-$p$ central class of the $p$-covering group of a $p$-quotient of the group (usually `group') found by a call to the `pq' program; \quad`workspace'& the workspace set for the `pq' process (either given as a second argument to `PqStart', or set by default to 10000000); \quad`menu'& the current menu of the `pq' process (the `pq' program is managed by various menus, the details of which the user shouldn't normally need to know about -- the `menu' field remembers which menu the `pq' process is currently ``in''); \quad`outfname' & is the file to which `pq' output is directed, which is always `ANUPQData.outfile', except when option `SetupFile' is used with a non-interactive function, in which case `outfname' is set to `"PQ_OUTPUT"'; \quad`pQuotient' & is set to the value returned by `Pq' (see~"Pq") (the field `pQepi' is also set at the same time); \quad`pQepi' & is set to the value returned by `PqEpimorphism' (see~"PqEpimorphism") (the field `pQuotient' is also set at the same time); \quad`pCover' & is set to the value returned by `PqPCover' (see~"PqPCover"); \quad`SP' & is set to the value returned by `PqStandardPresentation' or `StandardPresentation' (see~"PqStandardPresentation!interactive") when called interactively, for process <i> (the field `SPepi' is also set at the same time); \quad`SPepi' & is set to the value returned by `EpimorphismPqStandardPresentation' or `EpimorphismStandardPresentation' (see~"EpimorphismPqStandardPresentation!interactive") when called interactively, for process <i> (the field `SP' is also set at the same time); \quad`descendants' & is set to the value returned by `PqDescendants' (see~"PqDescendants"); \quad`treepos' & if set by a call to `PqDescendantsTreeCoclassOne' (see~"PqDescendantsTreeCoclassOne"), it contains a record with fields `class', `node' and `ndes' being the information that determines the last descendant with a non-zero number of descendants processed; \quad`xgapsheet' & if set by a call to `PqDescendantsTreeCoclassOne' (see~"PqDescendantsTreeCoclassOne") during an {\XGAP} session, it contains the {\XGAP} `Sheet' on which the descendants tree is displayed; and \quad`nextX' & if set by a call to `PqDescendantsTreeCoclassOne' (see~"PqDescendantsTreeCoclassOne") during an {\XGAP} session, it contains a list of integers, the <i>th entry of which is the <x>-coordinate of the next node (representing a descendant) for the <i>th class. \enditems \>ANUPQDirectoryTemporary( <dir> ) F calls the UNIX command `mkdir' to create <dir>, which must be a string, and if successful a directory object for <dir> is both assigned to `ANUPQData.tmpdir' and returned. The field `ANUPQData.outfile' is also set to be a file in `ANUPQData.tmpdir', and on exit from {\GAP} <dir> is removed. Most users will never need this command; by default, {\GAP} typically chooses a ``random'' subdirectory of `/tmp' for `ANUPQData.tmpdir' which may occasionally have limits on what may be written there. `ANUPQDirectoryTemporary' permits the user to choose a directory (object) where one is not so limited. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{Setting the Verbosity of ANUPQ via Info and InfoANUPQ} \>`InfoANUPQ' V The input to and the output from the `pq' program is, by default, not displayed. However the user may choose to see some, or all, of this input/output. This is done via the `Info' mechanism (see Chapter~"ref:Info Functions" in the {\GAP} Reference Manual). For this purpose, there is the <InfoClass> `InfoANUPQ'. If the `InfoLevel' of `InfoANUPQ' is high enough each line of `pq' input/output is directed to a call to `Info' and will be displayed for the user to see. By default, the `InfoLevel' of `InfoANUPQ' is 1, and it is recommended that you leave it at this level, or higher. Messages that the user should presumably want to see and output from the `pq' program influenced by the value of the option `OutputLevel' (see the options listed in Section~"Pq"), other than timing and memory usage are directed to `Info' at `InfoANUPQ' level 1. To turn off *all* `InfoANUPQ' messaging, set the `InfoANUPQ' level to 0. There are five other user-intended `InfoANUPQ' levels: 2, 3, 4, 5 and 6. \beginexample gap> SetInfoLevel(InfoANUPQ, 2); \endexample enables the display of most timing and memory usage data from the `pq' program, and also the number of identity instances when the `Identities' option is used. (Some timing and memory usage data, particularly when profuse in quantity, is `Info'-ed at `InfoANUPQ' level 3 instead.) Note that the the {\GAP} functions `time' and `Runtime' (see~"ref:Runtime" in the {\GAP} Reference Manual) count the time spent by {\GAP} and *not* the time spent by the (external) `pq' program. \beginexample gap> SetInfoLevel(InfoANUPQ, 3); \endexample enables the display of output of the nature of the first two `InfoANUPQ' that was not directly invoked by the user (e.g.~some commands require {\GAP} to discover something about the current state known to the `pq' program). The identity instances processed under the `Identities' option are also displayed at this level. In some cases, the `pq' program produces a lot of output despite the fact that the `OutputLevel' (see~"option OutputLevel") is unset or is set to 0; such output is also `Info'-ed at `InfoANUPQ' level 3. \beginexample gap> SetInfoLevel(InfoANUPQ, 4); \endexample enables the display of all the commands directed to the `pq' program, behind a ```ToPQ> ''' prompt (so that you can distinguish it from the output from the `pq' program). See Section~"Hints and Warnings regarding the use of Options" for an example of how this can be a useful troubleshooting tool. \beginexample gap> SetInfoLevel(InfoANUPQ, 5); \endexample enables the display of the `pq' program's prompts for input. Finally, \beginexample gap> SetInfoLevel(InfoANUPQ, 6); \endexample enables the display of all other output from the `pq' program, namely the banner and menus. However, the timing data printed when the `pq' program exits can never be observed. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{Utility Functions} \>PqLeftNormComm( <elts> ) F returns for a list of elements of some group (e.g.~<elts> may be a list of words in the generators of a free or fp group) the left normed commutator of <elts>, e.g.~if <w1>, <w2>, <w3> are such elements then `PqLeftNormComm( [<w1>, <w2>, <w3>] );' is equivalent to `Comm( Comm( <w1>, <w2> ), <w3> );'. *Note:* <elts> must contain at least two elements. \>PqGAPRelators( <group>, <rels> ) F returns a list of words that {\GAP} understands, given a list <rels> of strings in the string representations of the generators of the fp group <group> prepared as a list of relators for the `pq' program. *Note:* The `pq' program does not use `/' to indicate multiplication by an inverse and uses square brackets to represent (left normed) commutators. Also, even though the `pq' program accepts relations, all elements of <rels> *must* be in relator form, i.e.~a relation of form `<w1> = <w2>' must be written as `<w1>*(<w2>)^-1'. Here is an example: \beginexample gap> F := FreeGroup("a", "b"); <free group on the generators [ a, b ]> gap> PqGAPRelators(F, [ "a*b^2", "[a,b]^2*a", "([a,b,a,b,b]*a*b)^2*a" ]); [ a*b^2, a^-1*b^-1*a*b*a^-1*b^-1*a*b*a, b^-1*a^-1*b^-1*a^-1*b*a*b^-1*a*b*a^ -1*b*a^-1*b^-1*a*b*a*b^-1*a^-1*b^-1*a^-1*b*a*b^-1*a*b^-1*a^-1*b*a^-1*b^ -1*a*b*a*b*a^-1*b*a*b^-1*a*b*a^-1*b*a^-1*b^-1*a*b*a*b^-1*a^-1*b^-1*a^ -1*b*a*b^-1*a*b^-1*a^-1*b*a^-1*b^-1*a*b*a*b^2*a*b*a ] \endexample \>PqParseWord( <word>, <n> ) F parses a <word>, a string representing a word in the pc generators `x1,...,x<n>', through {\GAP}. This function is provided as a rough-and-ready check of <word> for syntax errors. A syntax error will cause the entering of a `break'-loop, in which the error message may or may not be meaningful (depending on whether the syntax error gets caught at the {\GAP} or kernel level). *Note:* The reason the generators *must* be `x1,...,x<n>' is that these are the pc generator names used by the `pq' program (as distinct from the generator names for the group provided by the user to a function like `Pq' that invokes the `pq' program). \>PqExample() F \>PqExample( <example>[, PqStart][, Display] ) F \>PqExample( <example>[, PqStart][, <filename>] ) F With no arguments, or with single argument `"index"', or a string <example> that is not the name of a file in the `examples' directory, an index of available examples is displayed. With just the one argument <example> that is the name of a file in the `examples' directory, the example contained in that file is executed in its simplest form. Some examples accept options which you may use to modify some of the options used in the commands of the example. To find out which options an example accepts, use one of the mechanisms for displaying the example described below. Some examples have both non-interactive and interactive forms; those that are non-interactive only have a name ending in `-ni'; those that are interactive only have a name ending in `-i'; examples with names ending in `.g' also have only one form; all other examples have both non-interactive and interactive forms and for these giving `PqStart' as second argument invokes `PqStart' initially and makes the appropriate adjustments so that the example is executed or displayed using interactive functions. If `PqExample' is called with last (second or third) argument `Display' then the example is displayed without being executed. If the last argument is a non-empty string <filename> then the example is also displayed without being executed but is also written to a file with that name. Passing an empty string as last argument has the same effect as passing `Display'. *Note:* The variables used in `PqExample' are local to the running of `PqExample', so there's no danger of having some of your variables over-written. However, they are not completely lost either. They are saved to a record `ANUPQData.examples.vars', i.e.~if `F' is a variable used in the example then you will be able to access it after `PqExample' has finished as `ANUPQData.examples.vars.F'. \>AllPqExamples() F returns a list of all currently available examples in default UNIX-listing (i.e.~alphabetic) order. \>GrepPqExamples( <string> ) F runs the UNIX command `grep <string>' over the {\ANUPQ} examples and returns the list of examples for which there is a match. The actual matches are `Info'-ed at `InfoANUPQ' level 2. \>ToPQLog([ <filename> ]) F With string argument <filename>, `ToPQLog' opens the file with name <filename> for logging; all commands written to the `pq' binary (that are `Info'-ed behind a ```ToPQ> ''' prompt at `InfoANUPQ' level 4) are then also written to that file (but without prompts). With no argument, `ToPQLog' stops logging to whatever file was being logged to. If a file was already being logged to, that file is closed and the file with name <filename> is opened for logging. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{Attributes and a Property for fp and pc p-groups} \>NuclearRank( <G> ) A \>MultiplicatorRank( <G> ) A \>IsCapable( <G> ) P return the nuclear rank of <G>, $p$-multiplicator rank of <G>, and whether <G> is capable (i.e.~`true' if it is, or `false' if it is not), respectively. These attributes and property are set automatically if <G> is one of the following: \beginlist%unordered \item{--} an fp group returned by `PqStandardPresentation' or `StandardPresentation' (see~"PqStandardPresentation"); \item{--} the image (fp group) of the epimorphism returned by an `EpimorphismPqStandardPresentation' or `EpimorphismStandardPresentation' call (see~"EpimorphismPqStandardPresentation"); or \item{--} one of the pc groups of the list of descendants returned by `PqDescendants' (see~"PqDescendants"). \endlist If <G> is an fp group or a pc $p$-group and not one of the above and the attribute or property has not otherwise been set for <G>, then `PqStandardPresentation' is called to set all three of `NuclearRank', `MultiplicatorRank' and `IsCapable', before returning the value of the attribute or property actually called. Such a group <G> must know in advance that it is a $p$-group; this is the case for the groups returned by the functions `Pq' and `PqPCover', and the image group of the epimorphism returned by `PqEpimorphism'. Otherwise, if you know the group to be a $p$-group, then this can be set by typing \){\kernttindent}SetFeatureObj( <G>, IsPGroup, true ); or by invoking `IsPGroup( <G> )'. Note that for an fp group <G>, the latter may result in a coset enumeration which might not terminate in a reasonable time. *Note:* For <G> such that `HasNuclearRank(<G>) = true', `IsCapable(<G>)' is equivalent to (the truth or falsity of) `NuclearRank( <G> ) = 0'. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \Section{Hints and Warnings regarding the use of Options} On a first reading we recommend you skip this section and come back to it if and when you run into trouble. \index{menu item!of pq program} \index{option!of pq program is a menu item} *Note:* By ``options'' we refer to {\GAP} options. The `pq' program also uses the term ``option''; to distinguish the two usages of ``option'', in this manual we use the term *menu item* to refer to what the `pq' program refers to as an ``option''. Options are passed to the {\ANUPQ} interface functions in either of the two usual mechanisms provided by {\GAP}, namely: \beginlist%unordered \item{--} options may be set globally using the function `PushOptions' (see Chapter~"ref:Options Stack" in the {\GAP} Reference Manual); or \item{--} options may be appended to the argument list of any function call, separated by a colon from the argument list (see Chapter~"ref:Function Calls" in the {\GAP} Reference Manual), in which case they are then passed on recursively to any subsequent inner function call, which may in turn have options of their own. \endlist Particularly, when one is using the interactive functions of Chapter~"Interactive ANUPQ Functions", one should, in general, avoid using the global method of passing options. In fact, it is recommended that prior to calling `PqStart' the `OptionsStack' be empty. The essential problem with setting options globally using the function `PushOptions' is that options pushed onto `OptionsStack', in this way, (generally) remain there until an explicit `PopOptions()' call is made. In contrast, options passed in the usual way behind a colon following a function's arguments (see "ref:Function Calls" in the {\GAP} Reference Manual) are local, and disappear from `OptionsStack' after the function has executed successfully. If the function does *not* execute successfully, i.e.~it runs into error and the user `quit's the resulting `break' loop (see Section~"ref:Break loops" in the Reference Manual) rather than attempting to repair the problem and typing `return;' then (since version {\GAP}~4.3), unless the error at the kernel level, the `OptionsStack' is reset. If an error is detected inside the kernel (hopefully, this should occur only rarely, if at all) then the options of that function will *not* be cleared from `OptionsStack'; in such cases: \beginexample gap> ResetOptionsStack(); #I Options stack is already empty \endexample is usually necessary (see Chapter~"ref:ResetOptionsStack" in the {\GAP} Reference Manual), which recursively calls `PopOptions()' until `OptionsStack' is empty, or as in the above case warns you that the `OptionsStack' is already empty. Note that a function, that is passed options after the colon, will also see any global options or any options passed down recursively from functions calling that function, unless those options are over-ridden by options passed via the function. Also, note that duplication of option names for different programs may lead to misinterpretations, and mis-spelled options will not be ``seen''. The non-interactive functions of Chapter~"Non-interactive ANUPQ Functions" that have `Pq' somewhere in their name provide an alternative method of passing options as additional arguments. This has the advantages that options can be abbreviated and mis-spelled options will be trapped. \index{troubleshooting tips} \>`ANUPQWarnOfOtherOptions' V is a global variable that is by default `false'. If it is set to `true' then any function provided by the {\ANUPQ} function that recognises at least one option, will warn you of ``other'' options, i.e.~options that the function does not recognise. These warnings are emitted at `InfoWarning' or `InfoANUPQ' level 1. This is useful for detecting mis-spelled options. Here is an example using the function `Pq' (first described in Chapter~"Non-interactive ANUPQ functions"): \begintt gap> SetInfoLevel(InfoANUPQ, 1); # Set InfoANUPQ to default level gap> ANUPQWarnOfOtherOptions := true;; gap> # The following makes entry into break loops very ``quiet'' ... gap> OnBreak := function() Where(0); end;; gap> F := FreeGroup( "a", "b" ); <free group on the generators [ a, b ]> gap> Pq( F : Prime := 2, Classbound := 1 ); #I ANUPQ Warning: Options: [ "Classbound" ] ignored #I (invalid for generic function: `Pq'). user interrupt at moreOfline := ReadLine( iostream ); Entering break read-eval-print loop ... you can 'quit;' to quit to outer loop, or you can 'return;' to continue \endtt Here we mistyped `ClassBound' as `Classbound', and after seeing the `Info'-ed warning that `Classbound' was ignored, we typed a <control>-C (that's the ```user interrupt at''' message) which took us into a break loop. Since the `Pq' command was not able to finish, the options `Prime' and `Classbound', in particular, will still be on the `OptionsStack': \begintt brk> OptionsStack; [ rec( Prime := 2, Classbound := 1 ), rec( Prime := 2, Classbound := 1, PqEpiOrPCover := "pQuotient" ) ] \endtt The option `PqEpiOrPCover' is a behind-the-scenes option that need not concern the user. Since {\GAP} 4.3, on `quit'ting the `break'-loop the `OptionsStack' is reset and a warning telling you this is emitted: \begintt brk> quit; # to get back to the `gap>' prompt #I Options stack has been reset \endtt Above, we altered `OnBreak' (see~"ref:OnBreak" in the Reference manual) to reduce the back-tracing on entry into a break loop. We now restore `OnBreak' to its usual value. \beginexample gap> OnBreak := Where;; \endexample *Notes* In cases where functions recursively call others with options (e.g.~when using `PqExample' with options), setting `ANUPQWarnOfOtherOptions := true' may give rise to spurious ``other'' option detections. It is recommended that the novice user set `ANUPQWarnOfOtherOptions' to `true' in their `.gaprc' file (see Section~"Loading the ANUPQ Package"). *Other Troubleshooting Strategies* There are some other strategies which may have helped us to see our error above. The function `Pq' recognises the option `OutputLevel' (see~"option OutputLevel"); if this option is set to at least 1, the `pq' program provides information on each class quotient as it is generated: \begintt gap> ANUPQWarnOfOtherOptions := false;; # Set back to normal gap> F := FreeGroup( "a", "b" );; gap> Pq( F : Prime := 2, Classbound := 1, OutputLevel := 1 ); #I Lower exponent-2 central series for [grp] #I Group: [grp] to lower exponent-2 central class 1 has order 2^2 #I Group: [grp] to lower exponent-2 central class 2 has order 2^5 #I Group: [grp] to lower exponent-2 central class 3 has order 2^10 #I Group: [grp] to lower exponent-2 central class 4 has order 2^18 #I Group: [grp] to lower exponent-2 central class 5 has order 2^32 #I Group: [grp] to lower exponent-2 central class 6 has order 2^55 #I Group: [grp] to lower exponent-2 central class 7 has order 2^96 #I Group: [grp] to lower exponent-2 central class 8 has order 2^167 #I Group: [grp] to lower exponent-2 central class 9 has order 2^294 #I Group: [grp] to lower exponent-2 central class 10 has order 2^520 #I Group: [grp] to lower exponent-2 central class 11 has order 2^932 #I Group: [grp] to lower exponent-2 central class 12 has order 2^1679 [... output truncated ...] \endtt After seeing the information for the class 2 quotient we may have got the idea that the `Classbound' option was not recognised and may have realised that this was due to a mis-spelling. The above will ordinarily cause the available space to be exhausted, necessitating user-intervention by typing <control>-C and `quit;' (to escape the break loop); otherwise `Pq' terminates when the class reaches 63 (the default value of `ClassBound'). If you have some familiarity with ``keyword'' command input to the `pq' binary, then setting the level of `InfoANUPQ' to 4 would also have indicated a problem: \begintt gap> ResetOptionsStack(); # Necessary, if a break-loop was entered above gap> SetInfoLevel(InfoANUPQ, 4); gap> Pq( F : Prime := 2, Classbound := 1 ); #I ToPQ> 7 #to (Main) p-Quotient Menu #I ToPQ> 1 #define group #I ToPQ> name [grp] #I ToPQ> prime 2 #I ToPQ> class 63 #I ToPQ> exponent 0 #I ToPQ> output 0 #I ToPQ> generators { a,b } #I ToPQ> relators { }; [... output truncated ...] \endtt Here the line ```\#I ToPQ> class 63''' indicates that a directive to set the classbound to 63 was sent to the `pq' program. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %% %E