Section Fold.
Variable B:Type.
Variable eqB:B->B->Prop.
Variable st:Equivalence eqB.
Variable f:A->B->B.
Variable i:B.
Variable Comp:Proper (eqA==>eqB==>eqB) f.

Lemma fold_right_eqlistA :
forall s s', eqlistA s s' ->
eqB (fold_right f i s) (fold_right f i s').