Convert between free group elements considering generator names.

[miguelmarco]

Right now, when we try to convert elements between free groups, they just get converted to the Tietze list, forgeting about the names of the generators. This can cause strange behaviour like:

sage: F.<a,b>=FreeGroup()
sage: G.<b,a>=FreeGroup()
sage: F(a) 
b

This patch solves this, looking for generators with matching names.

CC: @vbraun @sagetrac-sydahmad @videlec @jhpalmieri @sagetrac-tjolivet @rbeezer @dimpase @sagetrac-dshurbert

Component: group theory

Keywords: free groups

Author: Miguel Marco

Branch/Commit: 4a479ed

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/14684

[miguelmarco]

comment:1

Attachment: 14684_free_group_conversion.patch.gz

[videlec]

Branch: public/14684

[videlec]

comment:9

Hello,

I created a branch from the ticket with sage -dev. The review can starts from there.

What's the point of the following code in _element_constructor_?

if hasattr(P, '_freegroup_'):
    if P.FreeGroup() is self:
        return self.element_class(self, x.Tietze(), **kwds)

As far as I looked, there is no object in Sage with a _freegroup_ attribute.

Vincent

---

New commits:

b2d253d

Trac #14684: make conversion between free groups aware of generator names

[videlec]

Commit: b2d253d

[miguelmarco]

comment:10

It is an error. It should be _free_group (finitely presented groups have that attribute, that contains the free group after which they are defined).

Apparently it works even without that because the element_class init first tries to get the Tietze list anyways.

[videlec]

comment:11

So please, fix that!

[miguelmarco]

Changed branch from public/14684 to u/mmarco/ticket/14684

[miguelmarco]

Changed branch from u/mmarco/ticket/14684 to public/14684

[miguelmarco]

comment:14

Fixed.

[videlec]

Changed branch from public/14684 to u/mmarco/ticket/14684

[videlec]

Changed commit from b2d253d to 4a479ed

[videlec]

comment:15

Thanks. If it is, your commit should appear on this page... and it does not. I only see your commit at u/mmarco/ticket/14684 (public/14684 is one commit back). I switch back to the name of the branch that you used. If you want to commit to a specific branch use git push trac HEAD:public/14684.

Vincent

---

New commits:

4a479ed

Remved unnecessary check for _freegroup_

[videlec]

Reviewer: Vincent Delecroix

[videlec]

comment:16

Perfect!

Vincent

[vbraun]

comment:17

Author name should be real name, not trac username

[miguelmarco]

Changed author from mmarco to Miguel Marco

[miguelmarco]

comment:18

Sorry, i always forget those details.

[vbraun]

Changed branch from u/mmarco/ticket/14684 to 4a479ed