The composition of Bifunctors F and G, [x,y]F[G[x,y],G[x,y]], is a Bifunctor
Embed two Functors , one on each side
Embed one Functor to the left
Embed one Functor to the right
Extract the Functor on the first param.
The product of Bifunctors F and G, [x,y](F[x,y], G[x,y]), is a Bifunctor
Extract the Functor on the second param.
Unify the functor over both params.
A type giving rise to two unrelated scalaz.Functors.