3 Could not deduce `C [a]' from the context: ()
4 Probable cause: missing `C [a]' in instance declaration context
5 or missing instance declaration for `C [a]'
6 arising from an instance declaration at tcfail019.hs:18
9 Could not deduce `B [a]' from the context: ()
10 Probable cause: missing `B [a]' in instance declaration context
11 or missing instance declaration for `B [a]'
12 arising from an instance declaration at tcfail019.hs:18
14 Compilation had errors