fact: Definition extendable_isnull_fibers (n : nat) {A B} (f : A -> B) (C : B -> Type) : (forall b, ooExtendableAlong (const_tt (hfiber f b)) (fun _ => C b)) -> ExtendableAlong n f C.
imports: HoTT.Basics HoTT.Types Extensions NullHomotopy Modality