.. I.V. IIIA republishes I.V. III without the crappy formatting (my hour on the library computer ran out and then came Thanksgiving). Remember? …, 1010, 1011, 1000, 1001, 1110, 1111, 1100, 1101, 10, 11, 0, 1, 110, 111, 100, 101, 11010, 11011, 11000, 11001, 11110, ... Reprise: .. No other digits ==> binary .. Context free ==> “0” is always 0, “1” is always 1 ==> no minus sign even for negative integers .. Extrapolation, and considering that log2(21) = 4+ suggests a unique total unsigned representation .. Pairs, e.g. “0” “1”, “110” “111”, suggest radix or at least some kind of positional notation .. Aha: radix, base -2 .. In I.V. II, I mentioned, “Arithmetic? Looks dicey, but simple algorithms must exist, because indeed this is a familiar radix system (successive positions indicate successive powers of the so-called base).” Well, I know you have been slavering over that ever since (unless you worked it out for yourself). Subtraction is just a dialect of addition, really, and for