code: @GwtIncompatible // TODO
    public static long checkedSubtract(long a, long b) {
      long result = a - b;
      checkNoOverflow((a ^ b) >= 0 | (a ^ result) >= 0, "checkedSubtract", a, b);
      return result;
    }
docs: Returns the difference of {@code a} and {@code b}, provided it does not overflow.
  
  @throws ArithmeticException if {@code a - b} overflows in signed {@code long} arithmetic