WIP: Trivial SubmagmaWithOneNC has generators set to a list containing the trivial element

[FriedrichRober]

Description

The group returned by TrivialSubgroup had its generators set to an empty list. This is a problem for algorithms that want to access the generators of a group. Therefore I suggest to change the generators to be a list containing the trivial element in this case.

Old Behaviour:

gap> grp := TrivialSubgroup(Group((1,2,3,4),(1,2)));
Group(())
gap> GeneratorsOfGroup(grp);
[  ]
gap> GeneratorsOfGroup(Group(()));
[ () ]

Text for release notes

Calling SubmagmaWithOneNC with an empty list returns a group with generators set to a list containing the trivial element.

Further details

This issue was brought up by @DominikBernhardt in one of my repositories. gap-packages/WPE#14

Checklist for pull request reviewers

• proper formatting

• usage of relevant labels

  1. either release notes: not needed or release notes: to be added
  2. at least one of the labels bug or enhancement or new feature
  3. for changes meant to be backported to stable-4.X add the backport-to-4.X label
  4. consider adding any of the labels build system, documentation, kernel, library, tests

• runnable tests

• lines changed in commits are sufficiently covered by the tests

• adequate pull request title

• well formulated text for release notes

• relevant documentation updates

• sensible comments in the code

[ChrisJefferson]

This issue has been discussed previously ( #1239 , #4089 ).

It was decided that having an empty list of generators is acceptable. If you need an element of the group, you can explicitly take the identity.

[FriedrichRober]

Thanks for clarifying and linking the related issues.

Since it is already decided that an empty list is acceptable, I will close this pull request.