My personal opinion is that 'not' (Python-style) should be the operator instead, simply because it's easier to miss a ! than a 'not'. With that said, I'm with y

My personal opinion is that 'not' (Python-style) should be the operator instead, simply because it's easier to miss a ! than a 'not'. With that said, I'm with you in the 'not isEqual(a, b)' camp. The exception, imo, is functions that take boolean arguments. Languages should make it easy to show what they mean, and devs should take care to explain them. sort(reverse=true, numeric=false) is much easier to read than sort(true, false). (Silly example, it's meant to illustrate the general point, not to say anything about the signature of a sort() function.)