Find the hidden stones. Each port shows what happens to a beam fired in from there.
Absorbed: it ran straight into a stone.
Returned: it came back out of its own port.
1A pair: in at one port, out at the other.
A stone diagonally ahead turns the beam a quarter turn away from it.
Tap a cell — stone → dot → blank.
Tap a port — draws its beam past your stones.
Hint shows one deduction. Tap it again to apply.
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The board is solved when every stone is placed and every port matches. Once all the stones are down, a port that does not match is struck through.
Stones on both diagonals turn a beam back the way it came. A beam that would be turned before it enters the grid comes straight back out.
Arrows move over the cells and out onto the ports. Enter or Space marks a cell or traces a port. Z or Backspace undoes. H hints. Restart clears this puzzle; Undo restores it.