fact: Definition diagonal_functor : Functor (1 -> C) (D -> C) := @pullback_along _ D 1 C (Functors.to_terminal _).
imports: Category.Core Functor.Core NaturalTransformation.Core Functor.Composition.Core ExponentialLaws.Law1.Functors FunctorCategory.Core KanExtensions.Core InitialTerminalCategory.Core NatCategory Functor.Paths