pmc001.hs:14:1: warning: [-Wincomplete-patterns (in -Wextra)]
    Pattern match(es) are non-exhaustive
    In an equation for ‘f’:
        Patterns not matched:
            MkT1 MkT3
            (MkT2 _) MkT3
            MkT3 MkT1
            MkT3 (MkT2 _)

pmc001.hs:19:1: warning: [-Wincomplete-patterns (in -Wextra)]
    Pattern match(es) are non-exhaustive
    In an equation for ‘g’:
        Patterns not matched:
            MkT1 MkT3
            (MkT2 _) MkT3
            MkT3 MkT1
            MkT3 (MkT2 _)