Is there a way to lift a matrix in Sl2(Z/NZ) to SL2(Z) for an arbitrary N ?
I found this algorithm : here
But it seems to work only when N is prime. I think that the algorithm described in Shimura (which the implementation cited above is base on) works for arbitrary N. But I don't know how to modify the one above to make it work. Does anyone know how to do it.
Ultimately my goal is to iterate through a list of representatives of SL2(Z/24Z) in SL2(Z) so if anyone knows how to it without the above I would be equally (in fact probably more) grateful.