Isn't this just the negation of `eq_any`? This one is basically `\forall y \in args: x ≠ y`, whereas eq_any is `\exists y \in args: x = y` - wouldn't it make more sense to have, say `eq_any` and `eq_all` that you can later negate, so you'd get 4 possible functions if combined with `not` instead of only 2?