Fixpoint nsum (n:Nat) {struct n} : seq n Nat -> Nat :=
match n return (seq n Nat -> Nat) with
|O => fun x:seq 0 Nat => 0
|S m => fun x:seq (S m) Nat => (head x) + (nsum m (Seqtl x)) end.

Lemma Q8:forall(G:Setoid)(a:G)(A:part_set G)(n:Nat) (FINA:has_n_elements n A)(H:in_part a A),n>0.