Some new GP features
snfrank
snfrank compute the p-rank of a Smith normal form:
? snfrank([4,4,2], 2)
%82 = 3
? snfrank([4,4,2], 4)
%83 = 2
? snfrank([4,4,2], 8)
%84 = 0
? snfrank([4,4,2], 0)
%85 = 3