Once upon a time a logician accomplished a great deed, and the God-Emperor offered him a choice of rewards. “You may,” said the God-Emperor “have the hand of my eldest daughter, who is the heir to the throne, yet plain to look upon. Or you may take my youngest daughter, who is beautiful beyond words, but without inheritance.”
The next day, the God-Emperor caught the logician in bed with both his daughters. Enraged, he hurled threats and abuse at the scholar, who responded with a grin: “Guess someone never learned the difference between ‘or’ and ‘xor’.”
The God-Emperor ordered the logician brought to the throne room in chains, and told him “You have offended me and betrayed my generosity, so you will be subjected to trial by ordeal. I have placed in front of you seven chests. Six of the chests contain skulls. One of the chests contains the key to your chains. I have asked the most devious minds in my kingdom to prepare a logic puzzle giving hints as to which chest is which. You may open a single chest. If you do not find the chest with the key on your first try, you will be slathered in barbecue sauce and thrown to the wolves.”
The logician approached the chests, and upon each was written a clue in complicated logical notation. He examined all seven, and then stood a while, deep in thought. Finally, he opened the third chest. Inside was a golden key.
“Very impressive!” said the God-Emperor. Then he yelled “Guards! Slather this man in barbecue sauce and throw him to the wolves!”
“But…but!” babbled the terrified logician “…but you said…!”
The God-Emperor grinned. “Guess someone never learned the difference between ‘if’ and ‘iff’.”