What's the opposite of "is"?

``` if(myVariable is SomeType) ``` Out of nothing but curiosity, what's the opposite of that? I want to do something like: ``` if(!myVariable is SomeType) if(myVariable is not SomeType) ``` Neither compile. Given that "is" is a non-searchable word in most engines, this has been a hard one to find an answer to. Duplicate: C# : ‘is’ keyword and checking for Not