fact: Definition ispullback_symm {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.
imports: HoTT.Basics HoTT.Types HFiber PathAny Cubical.PathSquare Diagrams.CommutativeSquares