reserve a,b,c,h for Integer;
reserve k,m,n for Nat;
reserve i,j,z for Integer;
reserve p for Prime;

theorem Th61:
  for x being object holds
    x in multiples(i) implies x is Multiple of i
  proof
    let x be object;
    assume x in multiples(i);
    then ex m being Multiple of i st x = m;
    hence thesis;
  end;
