3步底线杀，a8 (a7)
li-05Kjq命名标签 (格·N)战术主题
底线：王被自己的兵困在底线——利用这一点。
引离：迫使防守的棋子离开岗位。
三步将杀：一段以将杀收尾的强制着法。
牵制：棋子一动，身后更有价值的目标就会暴露。
难度1086 ShuffleRating——俱乐部棋手水平。
白方走棋——找出最佳续着
How to recognize this tactic
A back-rank mate strikes when the king is boxed in by its own pawns and the back rank is under-defended. Check whether a rook or queen can reach the first rank with check and whether the only defender can be deflected or overloaded.
Deflection drags a defender away from its duty. Identify the enemy piece that guards a key square or mate, then force it to move — with a check, a capture or a threat it must answer — and strike where it no longer defends.
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.
A pin freezes a piece in front of a more valuable one behind it. Scan the ranks, files and diagonals your bishop, rook or queen controls: if an enemy piece cannot move without exposing its king or queen, it is pinned and can be piled on or bypassed.
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 g2, 车 a7, 马 f5, 兵 a2 f2 g3 h4。
黑方：王 g8, 车 c2, 象 d6, 马 e4, 兵 e5 c7 f7 g7 h7。
棋盘上有7枚白棋和9枚黑棋；该题局面出现在第29回合之后。
The position in numbers
Black are ahead by 4 points of material (12 against 16; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on g2, the black king on g8.
It is White to move on move 29, with 23 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 4 pawns, Black 5. Files fully open (no pawns of either colour): b, d — natural highways for the rooks and queen. Half-open for White: c, e.
The White king has 6 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
29. Ra8+ Bf8 30. Ne7+ Kh8 31. Rxf8#
为何奏效
- 好棋！车到a8保持压力（#2）。
- 好棋！马到e7保持压力（#1）。
- 好棋！车到f8保持压力（#）。
- 该变着以3步强制将杀结束。
- 若改走Bf8，则Ne7+，你仍占优。
Move by move
- 29. Ra8+ — 车 to a8 with check
- Bf8 — 象 to f8
- 30. Ne7+ — 马 to e7 with check
- Kh8 — 王 to h8
- 31. Rxf8# — 车 to f8 (capture) and it is checkmate
本题的题型
底线杀
王被自己的兵关在里面——重子直捣底线。
底线杀：国王被自己一排未动的兵关在后面，车或后突入底线一锤定音。识别特征：王前的兵没动过、没有通气口，底线只有一个守卫，甚至无人看守。常见手法是先引开或兑掉那个孤独的哨兵，再沿线突击。在自己的对局中要及时开气孔：一步兵着就能免除一场突发灾难。
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。
残局战术
残局里同样有战术——子力稀少时照样出击。
战术不会随着后的兑换而退休：捉双、牵制和双重攻击在残局里照样活跃。子力所剩无几，因此这里每一次战术损失几乎都直接定胜负。特征还是老几样：无保护的棋子、王与棋子同线、即将升变的兵。建议：即使在「纯技术」残局里，每步棋前也要搜一遍战术——自己的和对方的。
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 007
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