This image shows the position before White opts to play a Clearance Sacrifice, to get rid of White's Knight from b3 to c5; weaken Black's Queenside Pawns (they'll become Doubled on the c-file, following ...dxc5), then White's Queen can get closer to Black's King.
Clearance Sacrifice, Example 1
- ChessFlash Viewer -
White's Knight begins this example on a square that, ideally, he'd prefer his Queen to be on. So ...
Move 1, White makes the sacrificial Clearance move of his kNight, to c5; Black finds it too tempting to leave on the board and uses his d-file Pawn to capture (x) the Knight, on c5.
Move 2, White's Queen now has free access to b3.
Black's King is now in trouble, what with White's Queen now restricting escape across the b-file, together with White's Rook, lurking on e7.
Clearance Sacrifice, Example 1
- Video Example 1 (UPDATE: 22nd Nov. 2012) -
When I originally published this Clearance example, I saw a way for the game to result in a draw by Perpetual Check. Here's what I put:
Black's Nc8 can capture White's Re7, preventing Checkmate via Qb3-b7#. With even less Pieces, following said loss of White's Rook, White's chances of victory would be slim, but a draw by Stalemate could be achieved by Perpetual Check (three repeated Checks, in this case, with the Queen).
But, not having developed a good enough chess-brain (aye, still!), I couldn't see a way to get convert White's position into a win.
However, it's only recently (21st Nov. 2012) been brought to my attention that White can Mate in 6 Moves. The credit for the following example goes to a friend to this website, going by the alias of "Zan Zibar":
Zan Zibar explains about his use of the notation (M6, M3, _M1, etc.), here: [+]Show
From: Zan Zibar Date: Thu, Nov 22, 2012 at 3:42 AM Subject: Re: Clearance Sacrifice #1, could = M-6 for White...
>> I am replying concerning your first example of Clearance on your website.
Thank you for your prompt reply. My apologies for the delay in writing back. I can offer only two weak excuses - that my mail filtered your message into my spam folder since we hadn't corresponded before, and secondly, I wanted to prepare a pgn with all the variations of the M-6 with some notation.
It is really a straight-forward mate, but with enough subvariations as to make it's discussion problematic for a educational website such as yours. Nonetheless, it is a good example of clearance and if used you should at least refer to the M-6.
As you surmised M-6 stands for checkmate in 6 moves with best defense, less if opponent misplays. I believe it is a common shorthand, at least I use it as such.
In the pgn file I've pasted in below it is used extensively. I also use a notation like _M-#, where the _ (subscript) stands for sub-optimal. Meaning a subvariation where Black could have played a different move for a longer mate - at that point in the variation tree. It's a detail perhaps not worth elaborating, but for the sake of completeness here's an example
M4 ( M3 ( M2, _M1), M3 (M2), _M2 ), _M3 ( M2, M2, _M1 ) Best play here is M4, but _M3(_M1) is a 2 move checkmate.
My advice is to forget this detail if it hasn't already made sense to you! Apologies.
OK then, the moves follow. I've already complimented you on your site - let me once more thank you for both the content and the enjoyable whimsy it contains.