This may seem like a redundant command, but every time I want to negate isEqualTo I find myself going back to the start of an expression to put an ! and then putting parentheses around it.

But having a command that already returns the negated value is much more convenient.

_a notEqualTo _b which would be identical to !(_a isEqualTo _b)

This also makes sense, because we already have:
== and !=