{A B C D} {f : A -> B} {g : C -> D} {h : A -> C} {k : B -> D} (p : g o h == k o f) (pb : IsPullback (fun a => (p a)^)) : IsPullback p. Proof. rapply (cancelL_isequiv (equiv_pullback_symm g k)). apply pb. Defined.
Require Import HoTT.Basics HoTT.Types. Require Import HFiber Homotopy.IdentitySystems Cubical.PathSquare. Require Import Diagrams.CommutativeSquares.