More Gates (XOR, NAND & NOR)

Add an inversion bubble to a gate's output and you get its compound twin:

• NAND: AND then NOT. Output is 0 only when all inputs are 1.
• NOR: OR then NOT. Output is 1 only when all inputs are 0.
• XOR (exclusive OR): output is 1 when the inputs differ.

The little bubble on a symbol always means "invert this". Spotting it tells you half of what a gate does at a glance.