fact: Definition cancelL_mapinO {A B C : Type} (f : A -> B) (g : B -> C) : MapIn O g -> MapIn O (g o f) -> MapIn O f.
imports: HoTT.Basics HoTT.Types Equiv.BiInv Extensions HProp HFiber NullHomotopy Limits.Pullback PathAny Colimits.Pushout