2 tcfail001.hs:9: Warning:
3 Duplicate class assertion `A a' in the context: (A a, A a) =>
7 Couldn't match `[a]' against `t -> _116'
9 Inferred type: t -> _116
10 In an equation for function `op': op [] = []
11 In the definition for method `op'
14 Compilation had errors