not operator operator..

[S. Chancellor]

I really really hate the !in, !is syntax.   I think a lot of other 
people do too. I propose that the word not, become an operator on 
operators.  For example:

Foo not is null
Foo not in Bar

This not keyword will only function when it is part of these expressions:

EqualExpression
RelExpression
InExpression

As a consequence the following would be valid:

Foo not == Bar
Foo not <= Bar

-S.