Section map_fold_index.
Variables A B:Type.
Variable f:positive -> A -> B.
Variable c:B -> B -> B.
Variable u:B.
Hypothesis Hassoc : forall x y z:B,
c x (c y z) = c (c x y) z.
Hypothesis Hunit_left : forall x, c u x = x.

Lemma map_fold_index_lift_z : forall
(m:map A) (g:positive -> positive) (z:B),
map_fold_index' A B f c z g m =
c (map_fold_index' A B f c u g m) z.