reserve i for Nat, x,y for set;
reserve S for non empty non void ManySortedSign;
reserve X for non-empty ManySortedSet of S;

theorem Th1:
  for A,B being set
  for R being A-valued Relation
  holds R.:B c= A
  proof
    let A,B be set;
    let R be A-valued Relation;
    R.:B c= rng R & rng R c= A by RELAT_1:111,def 19;
    hence R.:B c= A;
  end;
