fact: Definition weqoverdnicoprod {n : nat} (P: ⟦S n⟧ → UU) : (∑ i, P i) ≃ (∑ j, P(dni lastelement j)) ⨿ P lastelement.
imports: UniMath.Foundations.NaturalNumbers UniMath.MoreFoundations.Tactics UniMath.MoreFoundations.DecidablePropositions UniMath.MoreFoundations.NegativePropositions