Church2.hs:27:14:
    Couldn't match expected type `CNat'
	   against inferred type `(a -> a) -> a -> a'
    In the first argument of `n', namely `(mul m)'
    In the expression: n (mul m) n1
    In the definition of `exp2': exp2 m n = n (mul m) n1

*** This error message is not helpful,
*** and the test should fail, not pass
*** These comments are here to make sure the output
*** doesn't match!