Description: Quotient map is a relation. Guarantees that QMap can be composed, restricted, and used in other relation infrastructure (e.g., membership in Disjs , Rels -based typing). (Contributed by Peter Mazsa, 12-Feb-2026)
|- Rel QMap R
|- Rel ( x e. dom R |-> [ x ] R )
|- QMap R = ( x e. dom R |-> [ x ] R )
|- ( Rel QMap R <-> Rel ( x e. dom R |-> [ x ] R ) )