Tantalizer 445: Key problem
19 September 2018
Posted by on
From New Scientist #996, 15th April 1976 [link]
Uncle Tom’s bungalow is well endowed with doors, as you can see. He locks them each night, to keep out things that go bump. He would dearly love to do it by passing through each door just once and locking it behind him, so as to finish safely locked up in his bedroom. Alas, it cannot be done. Ah, but wait a minute. It could be done, if he had one of the doors bricked up. By Jove, that’s it.
Precisely which door would he be better without?