reserve a,x,y for object, A,B for set,
  l,m,n for Nat;
reserve X,Y for set, x for object,
  p,q for Function-yielding FinSequence,
  f,g,h for Function;
reserve m,n,k for Nat, R for Relation;

theorem Th74:
  id(field R)*iter(R,n) = iter(R,n)
proof
  dom iter(R,n) c= field R by Th71;
  hence thesis by RELAT_1:51;
end;
