suggested coding topic

[John Cremona]

This would surely be a good time to sort out the multiple tickets
redoing the finite fields code in Sage. See #8333 and others (several
related patches in a sequence).

At the recent SD22 on elliptic curves people came up against a lot of
problems when doing a lot of reducing of curves over number fields
modulo primes, and this seems to be due to problems with the current
finite field setup.

I'll be there by Tuesday lunchtime!

[vdelecroix]

I have two elementary topics to suggest about matrix group...

1) The special linear groups over ZZ/nZZ work only for n prime. For
non prime n the constructor accepts the argument but an error is
raised after any operation
{{{
sage: G = SL(2, Zmod(4))
sage: print G
Special Linear Group of degree 2 over Ring of integers modulo 4
sage: list(G)
Traceback (click to the left of this block for traceback)
...
error coercing to finite field
}}}

2) Projective special linear groups are now only permutation groups...
it can be interesting to have them as matrices (one can easily define
canonic representant in GL or SL for classes in PGL or PSL).

(Those two topics are related to what I'm supposed to work on this
week: build general methods for computing and plotting fundamental
domains for subgroups of SL(2,ZZ) and other Fuchsian groups)