LEFT is "X-NOR" Gate and Right is "X-OR" Gate. EVERY input affects the output to change. It's good for 2-way switches or more, so it turns "OFF" or "ON" depends on the opposite as the output was.
INPUTS(BLUE LED) OUTPUT/RESULTS(RED LED)
X-NOR X-OR
- - + -
+- - +
-+ - +
++ + -
