proposition: Lemma cancelL_isembedding {A B C : Type} `{IsHSet B} {f : A -> B} {g : B -> C} `{IsEmbedding (g o f)} : IsEmbedding f.
proof: Proof. apply isembedding_isinj_hset. rapply (cancelL_isinjective (g:=g)). rapply isinj_embedding. Defined.
imports: Basics Types.Sigma Types.Forall Types.Paths Types.Unit Types.Arrow