From mathcomp.ssreflect Require Import seq.
Definition merge_func {A} (f1 f2:Z -> option A):
(BinNums.Z -> option A):=
fun ofs => if f1 ofs then f1 ofs else f2 ofs.

Lemma finite_ptree:
forall {A} (t:PTree.t A), exists b, forall b', (b < b')%positive -> (t ! b') = None.