reserve a, b, k, n, m for Nat,
  i for Integer,
  r for Real,
  p for Rational,
  c for Complex,
  x for object,
  f for Function;

theorem Th13:
  modSeq(m,n).1 = n mod modSeq(m,n).0
proof
  thus modSeq(m,n).1 = n mod (m mod n) by Def1
    .= n mod modSeq(m,n).0 by Def1;
end;
