tcfail001.hs:8:
    Warning: Duplicate class assertion `A a' in the context:
		 (A a, A a) => ...

tcfail001.hs:9:
    Couldn't match `[a]' against `t -> t1'
	Expected type: [a]
	Inferred type: t -> t1
    In an equation for function `op': op [] = []
    In the definition for method `op'