reserve i, j, k, l, m, n, t for Nat;

theorem Th10:
  k <= n implies 2 to_power n = (2 to_power k) * (2 to_power (n-'k ))
proof
  assume k <= n;
  then n = k + (n -' k) by XREAL_1:235;
  hence thesis by POWER:27;
end;
