theorem Th62:
  j in multiples(i) iff i divides j
  proof
    thus j in multiples(i) implies i divides j
    proof
      assume j in multiples(i);
      then j is Multiple of i by Th61;
      hence thesis by Def15;
    end;
    assume i divides j;
    then j is Multiple of i by Def15;
    hence thesis;
  end;
