fact: Definition prod_split {x y z w} (f : x ~{C^op}~> z) (g : y ~{C}~> w) : (x, y) ~{ (C ^op) ∏ C }~> (z, w) := (f, g).
imports: Category.Lib Category.Theory.Category Category.Theory.Functor Category.Construction.Opposite Category.Construction.Product