Three stones with a gap — (5,7), (7,7), (8,7), hole at (6,7) — are still a live three, and the power hides in the hole. Extending an end keeps it merely a three; filling the gap jumps a whole tempo ahead, completing the straight four (5,7)–(8,7) with both ends still open: an open four in a single move. That is why broken threes are beloved attackers — the defender must watch the ends AND the hole, and the hole is the one that kills. Find the one point that makes the open four.
Which single point gives an open four?
Finish this step to move on.