Solution
Chomp
Show the problem again
Players alternately eat a square from a rectangular chocolate bar (larger than 1×1), along with every square above and to the right of it. The bottom-left square is poisoned; whoever eats it loses. Which player wins with optimal play?
Worked solution
The first player wins, by a strategy-stealing argument: suppose the second player had a winning response to the first player eating just the top-right square. Then the first player could have achieved the resulting position directly on move one (any response to the top-right nibble is itself a legal first move), stealing the winning strategy: a contradiction. The proof is famously non-constructive: no general explicit strategy is known.
Source: Introduced by David Gale (1974); the divisor form is due to Fred Schuh (1952). Statement written for AxiomIQ.