Always false:
(x & !x) | (y & !y)
This is saying that for any set of inputs, the inputs for x and y have to be both be “x and y” and “not x and not y”. That doesn’t work.
Always true:
(x | y) | (!x | !y)
This is saying that it could be “x or y” or " not x or not y" . Any x or y works.
Is this fine? I just thought of the simplest ways to get always true and always false.