fact: Definition equiv_O_hfiber_functor_sigma (b:B) (v:Q b) : O (hfiber (functor_sigma f g) (b;v)) <~> O (hfiber f b).
imports: HoTT.Basics HoTT.Types Equiv.BiInv Extensions HProp HFiber NullHomotopy Limits.Pullback PathAny Colimits.Pushout