Fixpoint MapCanonicalize (m:Map A) : Map A :=
    match m with
    | M2 m0 m1 => makeM2 A (MapCanonicalize m0) (MapCanonicalize m1)
    | _ => m
    end.

Lemma MapMerge_canon : forall m m':Map A, mapcanon m -> mapcanon m' -> mapcanon (MapMerge A m m').