unit p where
    signature A where
        data A
    signature B(module B, A) where
        import A
    module P where
        import A
        import B
        type ZZ = A

unit r where
    module Impl where
        data A = A

unit q where
    dependency p[A=<A>,B=<B>]
    dependency r
    signature A(module A, A) where
        import Impl(A)
    signature B(module B, A) where
        import Impl(A)
    module M where
        import A
        import B
        import P
        type AA = A
        f :: ZZ -> AA
        f x = x