fact: Definition weqstnsum1_prelim {n : nat} (f : ⟦n⟧ -> nat) : (∑ i, ⟦f i⟧) ≃ ⟦stnsum f⟧.
imports: UniMath.Foundations.NaturalNumbers UniMath.MoreFoundations.Tactics UniMath.MoreFoundations.DecidablePropositions UniMath.MoreFoundations.NegativePropositions