[math-fun] Puzzle: Where was the white king?

Cute! (I detect two solutions; another piece could be added to prevent a second option.) I'm still very fond of a retrograde chess problem from a Martin Gardner column, attributed to Raymond Smullyan: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . r . b . . . . B . . . . . . . . . . . . . . . . . . . . . . . . . . k . . . . After a legal move has been completed in a legal chess game, the white king was accidentally knocked off the board. Puzzle: Where was the white king? (No fair if you've already seen this.) —Dan

From: Bill Gosper <billgosper@gmail.com>

r3k3/p1p5/Q3K3/8/8/8/8/8 w --rwg