truth machines


A certain machine intelligence company has invented a remarkable series of machines. They are called truth machines. For any statement that is input, the machines will indicate the truth-value of the statement with a flashing light -- either green or red. The truth machines are manufactured in both the UK and Australia, but look identical since they are built according to the same design -- yet there is an important difference: the machines built in the UK indicate "true" with a green light and "false" with a red light, while the machines built in Australia do it the other way round.


Below are the three machines A, B, and C. One was built in the UK and one was built in Australia. It's unknown where the third machine was built, but we know for sure that it is broken: it will randomly flash a red or green light when any statement is input.







The problem is that we've lost track of which ones are which.


Your task is to determine which machine was built in the UK, which was built in Australia, and which one is broken. (And, of course, you should try to do so in the most elegant and efficient way.)


** Page created and maintained by B. Rabern **

Based off of the puzzles of Raymond Smullyan.

Smullyan 1997, The Riddle of Scheherazade, (Chapter XVIII).