Subtraction Is Functionally Complete

>Our resulting truth table is equivalent to ... the IMPLY gate ... It turns out this truth table is functionally complete

No it isn't? The link provided even explains that NAND and NOR gates are the only functionally complete boolean operators. Technically an extra operation/circuit sneaks in when the writer constructs NOT by feeding a signed -0 i.e. F

Beautiful. This would make an excellent build target for a 'virtualized hardware' system in-silico.