(September 10, 2015 at 12:12 pm)Napoléon Wrote: You ask the one guard what door the other guard would point to if you were to ask him to point to the freedom door, and work it out from there.
Indeed if you ask any guard wich door his fellow guard would point as the freedom door, the answer is always false as per the no contradiction law. In the end, it is a modus ponens, from a reductio.