3步杀：捉双，d4
li-00rw0战术主题
捉双：一子同时攻击两个目标——无法两全。
三步将杀：一段以将杀收尾的强制着法。
难度1729 ShuffleRating——适合进阶战术爱好者。
白方走棋——找出最佳续着
How to recognize this tactic
A fork is one piece attacking two targets at once. Look for a knight, pawn or queen move that lands where it hits the king (or a bigger piece) and a second undefended unit on the same turn — the opponent can save only one.
In a mate in three every move must be forcing; the defender should never get a free tempo. Find the check or threat that herds the king, calculate the single defence to each, and confirm the net closes on the third move.
General method: before you move, list the forcing candidates — every check, every capture, every direct threat — and calculate those first. The solution to a tactic is almost always among them.
棋盘上的局面
白方：王 g1, 后 g4, 象 g3 g6, 兵 b2 c2 h5 f7。
黑方：王 h8, 后 d8, 车 a8, 象 d4, 马 c6, 兵 a4 b4 d5 g5 h6。
棋盘上有8枚白棋和10枚黑棋；该题局面出现在第40回合之后。
The position in numbers
Black are ahead by 6 points of material (19 against 25; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on g1, the black king on h8.
It is White to move on move 40, with 6 legal replies to weigh — only the line that keeps the advantage solves the puzzle. White are in check right now, so every reply must answer the check.
White keeps 4 pawns, Black 5. Files fully open (no pawns of either colour): e — natural highways for the rooks and queen. Half-open for White: a, d, g.
White hold the bishop pair, an edge in open lines. The White king has 4 empty squares to step to right now — the fewer they are, the closer a mating net.
解答与讲解
主要变着
40. Qxd4+ Nxd4 41. Be5+ Qf6 42. Bxf6#
为何奏效
- 好棋！后到d4保持压力（#2）。
- 好棋！象到e5保持压力（#1）。
- 好棋！象到f6保持压力（#）。
- 该变着以3步强制将杀结束。
- 若改走Nxd4，则Be5+，你仍占优。
Move by move
- 40. Qxd4+ — 后 to d4 (capture) with check
- Nxd4 — 马 to d4 (capture)
- 41. Be5+ — 象 to e5 with check
- Qf6 — 后 to f6
- 42. Bxf6# — 象 to f6 (capture) and it is checkmate
本题的题型
角落杀
被逼进角落的王，再也没有落脚的格子。
角落杀：国王被赶进棋盘一角，那里他只有三个相邻格——而它们全被夺走或占据。角落是国王最糟糕的住所：进攻方需要控制的格子最少。用将军把国王往角落里赶，绝不让他溜回中心。在最后一击之前切断所有逃亡路线——将杀几乎会自己成形。
唯一着法
其他任何一步都会输——找到唯一撑得住的那一步。
唯一着法：除了独一无二的那步棋，其余全输的局面。这里不能「顺手」下棋：把原则上不同的防守都过一遍——逃跑、垫挡、兑换、反击——再淘汰被驳倒的。这类题目的标志：显而易见的着法很快就输，而正解常常看起来古怪。先弄清威胁你的究竟是什么——那步唯一的防守自会现身。
三步杀
三步之内的强制将杀。
三步杀是一道强制的阶梯：你的每一步都收窄对手的选择，第三步画上句号。到将军和弃子中寻找开局之着：杀题里安静的首着虽少见，却格外阴险。脑中要有变化树：每种防守对应自己的分支。别在第二步就停下——最终的将杀图景必须亲眼算到。
来源
源自 Lichess 题库（CC0）。
经 Stockfish 深度 20+ 验证。
解法强制性已确认（verified）。
题包 013
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