{-# LANGUAGE TypeFamilies #-}

unit p where
    signature H where
        type family Elem c

unit q where
    signature H where
        type family Elem c

unit r where
    dependency p[H=<H>]
    dependency q[H=<H>]
    module M where
        import H
        type instance Elem Bool = Int

unit h-impl where
    module H where
        type family Elem c
unit s where
    dependency r[H=h-impl:H]