Liar'sParadox |
Shown to the right is one of the many variants of what is known as the Liar's Paradox. It is self-explanatory and is a non-trivial example of thinking in truth tables. The answer is at the bottom, so don't look there if you want to solve it yourself.
This is included for laughs; and, in case you ever find yourself in a place where there are people who tell the truth as well as your garden variety liars.