Functional completeness: NOT, OR, AND from NOR — NOR gate

Why this example is worth doing

NOR is universal exactly as NAND is, but the gate counts are transposed: AND is the expensive one here at three gates while OR costs two. That asymmetry decides real designs — a function whose minimal form is a product of sums maps cheaply onto NOR and expensively onto NAND, and vice versa. The page states the rule of thumb that SOP suits NAND and POS suits NOR, which is the single most useful thing to remember about the two families.

Try your own input in the NOR gate. Truth table, symbol and algebraic form for (A + B)′, the other universal gate.