# basic math...well, maybe 6502 assembly math

April 13, 2004
Geekery of the Moment
Math oddity: it hit me last night that subtraction is more powerful than addition, because if you do enough subtractions (from zero) you can do addition, but there's no way to do subtraction by doing a lot of additions. For example, if I want to add 3 and 5, I could subtract 3 from zero (-3), subtract 5 from that (-8), then subtract that total from zero (8). But I can't think of anyway of doing subtraction via addition, except for saying "add the negative of" which seems to be quietly invoking multiplication or worse. (This hit me because of Assembly Programming, where often subtracting a number from zero is the easiest way to get the negative of a number, and you have to do slightly different setup before adding than you do for subtracting.)

There's a parallel thing with division being able to emulate multiplication but not vice versa, though it breaks down when one of the numbers is zero.

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