Definition concatenate' {X:UU} {m n:nat} (f : ⟦m⟧ -> X) (g : ⟦n⟧ -> X) : ⟦m+n⟧ -> X. Proof. intros i. induction (weqfromcoprodofstn_invmap _ _ i) as [j | k]. + exact (f j). + exact (g k). Defined.
Require Import UniMath.MoreFoundations.Tactics. Require Import UniMath.MoreFoundations.DecidablePropositions. Require Import UniMath.MoreFoundations.NegativePropositions.