mathlib

fb7dfa16 - feat(data/{nat,int,zmod,finset}): add a few useful facts (#1220)

feat(data/{nat,int,zmod,finset}): add a few useful facts (#1220) * feat(data/finset): add a few useful facts * feat(data/zmod/basic): express neg in terms of residues * feat(data/{nat,int}): add theorem 'mod_mod_of_dvd'