FlipSight : Extraction: Preparing to Block the Square Next to the Corner

A swindle is when a corner and the C-square next to it are both empty and the opponent cannot enter the C-square even after you take the corner. If an opponent disc is on the X-square, you can take the corner along the diagonal. But if there is an opponent disc (a foothold) on the line running from the C-square toward the X-square, the opponent flanks that line and enters the C-square as soon as you take the corner. Extraction is a move that removes this foothold first to set up a swindle.

You remove footholds from the line one at a time by flipping them along another line, such as a diagonal, not along that line itself. If no opponent disc remains on the line, the whole line becomes yours when you take the corner and flip the X-square, so the opponent cannot play the C-square. If there are two or more footholds, the next disc becomes a new foothold once you remove one, so plan the order and remove them all. Also check that your move does not create a new foothold on another line.

Black to move. The two squares A8 and B8 remain as a pair, and there is a White disc on the X-square B7. If Black takes A8 now, B7 turns black, but White plays B8 and flanks B7 and B6 along column B. The White disc B5 on column B is White's foothold. Use ▶ to play it (Black A8 → White B8).

In the same position, Black F1 flips E2, D3, C4 and B5 along the diagonal and removes the single foothold B5 from column B. White can only play F2, and when Black takes A8, column B is all black, so White cannot enter B8 (a swindle). Use ▶ to play it (Black F1 → White F2 → Black A8).

Black to move. If Black takes H8 now, White plays G8 and flips G7 back, so Black must remove both footholds on column G, G5 and G6. Black removes G5 along the diagonal with C1 and, after White passes, G6 along row 6 with A6, and the two moves can be played in either order. Wherever White plays, once Black takes H8, column G is all black and White cannot enter G8. Use ▶ to play it (Black C1 → White passes → Black A6 → White B3 → Black H8).

Exercise

Black to move. If Black takes A1 now, White can enter the C-square B1 next to it. Find the move that removes a White foothold so that White cannot play B1 after Black takes A1.

Exercise

White to move. If White takes H1 now, Black can enter the C-square G1 next to it. Find the move that removes a Black foothold so that Black cannot play G1 after White takes H1.

Exercise

White to move. If White takes H8 now, Black can enter the C-square H7 next to it. Find the move that removes a Black foothold so that Black cannot play H7 after White takes H8.

Exercise

White to move. If White takes H1 now, Black can enter the C-square G1 next to it. Remove all of Black's footholds on column G in two moves.

Exercise

White to move. If White takes H1 now, Black can enter the C-square H2 next to it. Remove all of Black's footholds in two moves.