use And, Or, Not gates only

And finally, since DeMorgan's laws allows us to write "or" in terms of "not" and "and", and the latter to can be written in terms of NAND alone, so too can "or" be written in terms of NAND alone. And this leads to a manufacturing question: is having only one type of gate, but using more of them, cheaper than having many types, and using fewer? An important aspect of computers is their ability to add binary digits: 0 + 0 = 00, 0 +1 = 01, 1 + 0 = 01,1 + 1 = 10. We can represent this as a truth table with two inputs and two outputs: the inputs X1, X2 are the two one-digit binary numbers we want to add, while the outputs y. Y2 are the two digits of the output. Draw up a circuit diagram for this; it's called a "half-adder". y2 x, x ya 0 0 0 0 1 0 1 0 0 1 1 1 0 1 1 0