proposition: Theorem equiv_sigma_fibration_O@{u v} `{Univalence} {O : Subuniverse} {Y : Type@{u}} : (Y -> Type_@{u v} O) <~> { p : { X : Type@{u} & X -> Y } & MapIn O p.2 }.
proof: Proof. refine (_ oE (equiv_sig_coind@{u v u v v v u} _ _)^-1). apply (equiv_functor_sigma'@{v u v v v v} equiv_sigma_fibration@{u v}); intro P; cbn. rapply equiv_forall_inO_mapinO_pr1. Defined.
imports: HoTT.Basics HoTT.Types HFiber Limits.Pullback Pointed Truncations