Lemma xb0_ind:forall (m:fmap)(x:dart), inv_hmap m -> succ m zero x -> let x0 := cA m zero x in let x_1:= cA_1 m one x in let xb0:= bottom m zero x in let xh0:= top m zero x in let xh0_1:= cA_1 m one xh0 in let p := MF.Iter_upb m xh0_1 in xb0 = Iter (cF m) (p-1)%nat xh0_1.