Testing for congruence in Haskell

Hello /prog/ Haskell programers users. Is it possible to test for the congruence of expression in Haskell? I know i can say
this a = if (a 12) == 12 then (a 12) else (a 13)
and expect this (\ x -> x + 1) to eval to 14. But is there anyway to test for the equivalence of two (or more) expressons without actually applying either of them? In other words, can haskell do anything with thunks, aide from than apply them?

(\ x -> x) == (\ x -> x) is not an expression. Is there a corrext syntax for this type of thing?
Thanks,

>>10
Steve Jobs!?