(** [MapInter], [MapRngRestrTo], [MapRngRestrBy], [MapInverse] not implemented: need a decidable equality on [A]. *)
Fixpoint MapDelta (m:Map) : Map -> Map :=
match m with
| M0 => fun m':Map => m'
| M1 a y =>
fun m':Map =>
match MapGet m' a with
| None => MapPut m' a y
| _ => MapRemove m' a
end
| M2 m1 m2 =>
fun m':Map =>
match m' with
| M0 => m
| M1 a' y' =>
match MapGet m a' with
| None => MapPut m a' y'
| _ => MapRemove m a'
end
| M2 m'1 m'2 => makeM2 (MapDelta m1 m'1) (MapDelta m2 m'2)
end
end.

Lemma MapDelta_semantics_2_1 :
forall (a:ad) (y:A) (m':Map) (a0:ad) (y0:A),
MapGet (M1 a y) a0 = None ->
MapGet m' a0 = Some y0 -> MapGet (MapDelta (M1 a y) m') a0 = Some y0.