fact: Definition flatten' {X:UU} {n:nat} {m: ⟦n⟧ -> nat} : (∏ (i: ⟦n⟧ ), ⟦m i⟧ -> X) -> ( ⟦stnsum m⟧ -> X).
imports: UniMath.Foundations.NaturalNumbers UniMath.MoreFoundations.Tactics UniMath.MoreFoundations.DecidablePropositions UniMath.MoreFoundations.NegativePropositions