People, this is a question about Standard library. I write module _ {α α=} (R : CommutativeRing α α=) (open CommutativeRing R using (0#; 1#; ...)) (0≉1 : ¬ 0# ≈ 1#) ... But probably 0≉1 needs to be an axiom in RingWithOne (and in CommutativeRing). Is such in Standard library? Thanks, ------ Sergei