Section MapC.
Variables A B C : Type.

Lemma MapDomRestrBy_By_comm_c :
forall (m:Map A) (m':Map B) (m'':Map C),
mapcanon A m ->
MapDomRestrBy A C (MapDomRestrBy A B m m') m'' =
MapDomRestrBy A B (MapDomRestrBy A C m m'') m'.