How do you express logical negation in a circuit?

Question

In C and C ++ ! denies the result:

 if( !( a == b ) ) 

In the diagram, I found only eq? . How to say "not equal"? Or should we say bluntly

 (eq? #f (eq? expr expr)) 

Answer 1

The circuit has not , so you can do: (not (eq? expr expr))

Answer 2

Could you try to guess?

 (not #f) ==> #t