Section MapC.
Variables A B C : Type.

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