Square Logic ala Taxicab Geometry
An old gentleman used to take a daily walk around the block. So regular was he that his neighbors would set their clocks by him.
One day he failed to pass a certain house. Next day the houseowner, meeting the old gentleman on the street, asked him whether he had been ill the day before.
"Oh, no," he answered, "I'm just getting too old and feeble to walk the whole way around the block. so now I walk halfway around and then turn around and go home again."
Source: H. Larsen, Jokes and Riddles, Row, Peterson & Co., 1956