fact: Definition first {x y z : C} (f : x ~> y) : x ⨂ z ~> y ⨂ z := fork (f ∘ proj_left) proj_right.
imports: Category.Lib Category.Theory.Category Category.Theory.Isomorphism Category.Theory.Functor Category.Structure.Monoidal.Relevance Category.Structure.Monoidal.Semicartesian