Regression in DeclareHandlingByNiceBasis/InstallHandlingByNiceBasis

[zickgraf]

The documentation of DeclareHandlingByNiceBasis/InstallHandlingByNiceBasis claims:

name must be a string, a filter f with this name is created, and a logical implication from f to IsHandledByNiceBasis (61.11-6) is installed.

This is not true anymore since commit 2f4a518 (see 2f4a518#diff-14aba9b3712179af58d64fc6572ca6107a7c746245c8c795a98b79ec746676d4R690-L694).

This leads to an error when loading QPA2:

Error, required filters [
    "IsSubspaceOfQPAVectorSpace" 
]
for 1st argument do not match a declaration of NiceFreeLeftModule called from
<<compiled GAP code>> from GAPROOT/lib/oper1.g:336 in function InstallMethod called from
<function "InstallMethod">( <arguments> )
 called from read-eval loop at QPA2/lib/vecspace.gi:766
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue

I'm not sure if the documentation or the regressing commit should be updated.

[ThomasBreuer]

@zickgraf Yes, the new filter f is now just a flag such that f and IsFreeLeftModule and IsAttributeStoringRep implies IsHandledByNiceBasis. I think this is an improvement over the situation before #3006 got merged, and I am going to update the documentation accordingly.

The mentioned problem in the QPA2 package arises from the fact that the NiceFreeLeftModule method wants to be applicable as soon as the argument is in IsSubspaceOfQPAVectorSpace, which does no longer imply IsFreeLeftModule.
(Most of the vector spaces types in the GAP library use the generic NiceFreeLeftModule method, that's why I had overlooked this problem.)
If it is acceptable to adjust the QPA2 code then I would suggest to change the InstallMethod call such that IsFreeLeftModule and IsSubspaceOfQPAVectorSpace is required.

[zickgraf]

If it is acceptable to adjust the QPA2 code then I would suggest to change the InstallMethod call such that IsFreeLeftModule and IsSubspaceOfQPAVectorSpace is required.

I have created a PR: sunnyquiver/QPA2#44 I'm not the author of QPA2, so I'm not 100% sure that this will be accepted, let's see.

[zickgraf]

Fixed by #5336.