Definition compatible m1 m2 := forall k v1 v2, m1 k = Some v1 -> m2 k = Some v2 -> v1 = v2.Global Instance compatible_refl : Reflexive compatible.Global Instance compatible_comm : Symmetric compatible.

Lemma compatible_incl : forall m1 m2 m (Hcompat : compatible m2 m) (Hincl : map_incl m1 m2), compatible m1 m.