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Joel Benjamin vs Mephisto (Computer)
Simul, 31b (1987) (exhibition), ?
Gruenfeld Defense: Russian. Smyslov Variation (D99)  ·  1-0

ANALYSIS [x]

FEN COPIED

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Kibitzer's Corner
< Earlier Kibitzing  · PAGE 2 OF 2 ·  Later Kibitzing>
Feb-06-18  Walter Glattke: Also mating with 35.Bf5+ Kf7 36.e6+,
e.g. 36.-Kg8 37.e7 Rf8 38.Bf6+ Rf7 e8Q/R#
Feb-06-18  SandyJames: Is this called a clearance sacrifice?
Feb-06-18  Steve.Patzer: I got it easily. Is Tuesday the easy day?
Feb-06-18  yadasampati: <SandyJames> I think this is a deflection sacrifice. A clearance sacrifice is one where the sacrificed piece itself is in the way. A deflection sacrifice forces an opposing piece to leave a certain square.
Feb-06-18  cocker: I'm afraid I went for 36 R7h5, which also works, but takes three more moves.
Feb-06-18  mel gibson: < stst: the Black K is doomed almost any way.>

Yes - I overlooked the checkmate as I was
too busy proving that I could Queen one of the 2 passed pawns. The answer is yes & Black cannot win.

Feb-06-18  Whitehat1963: Never found it.
Feb-06-18  jith1207: Is there a name perhaps for this check mate?

Where the mating pieces are supported by each other *through* the opponent king?

Feb-06-18  gofer: Well, I first looked at <36 Bf5+ Kf7 37 e6+ Kf6/Kf8/Kg8 38 Rxg7 Kxg7 39 e7 > which seems to be fine.


click for larger view

I then saw the checkmate and thought that "fine" wasn't quite good enough.

Feb-06-18
Premium Chessgames Member
  perfidious: <yadasampati>, a deflexion sacrifice may also force an enemy piece or pawn to occupy a square.
Feb-06-18  malt: <36.R1h6+> Deflects the bishop, 36...B:h6 37.Bf5#
Feb-06-18  TheTamale: Mephis-"d'oh!!"
Feb-06-18  patzer2: For a forced mate-in-two or three, I now generally classify it as such without worrying about whether it involves supporting tactical elements such as deflection, decoy or clearance.

However, it does seem to me the mate-in-two 36. R1h6+! Bxh6 37. Bf5# does combine elements of deflection (forcing a piece away from a specific square), clearance (forced removal of a piece from a rank, file or diagonal) and possibly decoy (forcing a piece to a specific square).

In this case, 36. R1h6+ forces the Bishop away from g7 (deflection) and forces it to h6 (decoy) which clears the seventh rank for the Rook on h7 to cover the flight square f7 (clearance). So after 36. R1h6+! forces 36...Bxh6, White has 37. Bf5# (mate-in-two).

P.S.: One could also argue it involves the X-ray tactic as the Bishop after 37. Bf5# not only checks the King, but also X-rays the opposing monarch on g6 to defend the Rook on h7 which covers the previously available flight square on f7. With the King in check after 37. Bf5#, it's checkmate because the King is in check, has no flight square and cannot capture or block the checking piece.

Feb-06-18  Pasker: I knew it will be a rook move for sure but which rook to sacrifice? That's was the only question. After some thought I found the checkmate. Nice finish!
Feb-06-18  waustad: There appear to be other wins, but mate in 2 is a lot better.
Feb-06-18  morfishine: This combination uses a deflection tactic forcing Black's DSB off the 7th rank (but neither a clearance nor a decoy tactic is utilized here)

[*decoying is the tactic of ensnaring a piece, usually the king or queen, by forcing it to move to a poisoned square with a sacrifice on that square]

In this example, the Black King gets mated but doesn't move, so its not a decoy.

A 'clearance' sac is used when one of your own pieces is in the way of another of your pieces. The piece "in the way" moves or 'clears out' allowing the other piece to use the now empty square. By occupying the vacated square, it becomes markedly more effective.

Striking examples are when Queens or rooks are sacrificed so a Knight or Bishop can use the square to deadly effect

I like this one, White has a deadly clearance sac:


click for larger view

*****

Feb-06-18  pao13: Arrgh...
As usual,I miss the mate sequence.I saw
only that:1.Bf5+ Kf7
2.Rxg7+ Kxg7
3.Rg8+ Kg8(...Kf8 3.Rh8+xd8)
4.Rxb7 and then e6-e7+-
But why torment ourselves?Mate is way faster!Waiting for the next...
Feb-06-18  Marmot PFL: 36 Rh1-h6+ leads to mate. From back when it was fun to play computers. They didn't usually learn from their losses either, so once you found a way to beat a program you could do it several times before the programmers wised up.
Feb-06-18  saturn2: <morfishine I like this one> Me too 1 Qe6 N(orB)xQ 2 Nh6
Feb-06-18
Premium Chessgames Member
  Breunor: Also went with 37 Bf5 ch. Kf7 38 e6 ch which Stockfish shows as +55 or so but not as good as mate in 2.
Feb-06-18  Mayankk: I only spotted the Bf5, e6 line as well. I knew there was a quick mate somewhere there for sure but couldn’t quite make it work.

And it all seems so easy once you see the mate-in-two solution.

Feb-06-18  thegoodanarchist: Took me longer than it should have. Next time I better eat my Wheaties.
Feb-06-18  NBZ: It is nice to see a computer being destroyed in such patzer-like fashion. Ah the good old days of the Berlin Wall.
Feb-07-18  SandyJames: Thanks <morfishine>
Feb-07-18  SandyJames: Thanks <yadasampati>
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