On Thursday, February 5, 2026 at 12:15:21 PM UTC+1  wrote:

As a workaround, I think that explicitly converting the gap list returned 
by libgap.RightTransversal(W, G) into a python list helps.  I.e.,

list(libgap.RightTransversal(W, G))

Martin


I use this initially also for G=trivial (basically I am trying to 
incrementally build the stabilizer of something by iterating over the 
cosets of a stabilizing group already found) so constructing a list  of 
which only a small part will be consumed is a bit inconvenient. However 
your issue suggests to use

for i in range(0, len(R)):
  w = W(R[i])

This seems to work perfectly!

I must say that I am mildly surprised that this works. I was guessing that 
the coset representatives would be found on the fly in some way.

In any case: thanks for investigating and filing the issue!

Best,
Michel


On Thursday, 5 February 2026 at 11:16:52 UTC+1 Martin R wrote:

That's a huge example.

sage: len(libgap.RightTransversal(W, G))
138240

I think it is a gap bug, I am checking right now.


On Thursday, 5 February 2026 at 07:46:47 UTC+1 wrote:

> This is very strange code - you are attempting to change the variable of 
a loop inside a loop. 
>
> What do you mean to do here? 
>
> Dima

Well that's not the point. Writing v=W(w) gives the same bug...

Best,
Michel

PS. This was just some quick test code, but this being said, I think 
assigning to a loop variable is fine. This does not influence the state of 
the iterator. A quick test confirms this.




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