But how to get another white piece near the passed pawn? All the roads to c7 seem to be blocked.

So it seems we are looking for a breakthrough sacrifice. The most forcing moves don't seem to work. Qxa6 might be fun if the black queen and king rook were distracted, but it doesn't work yet. Hmmm ... store that one for later.

After casting around for a while I notice the VTOL move Rd8. Okay, okay, so it's not exactly legal, but wouldn't it be great if we could play it?

That leads to a fantasy about opening the d file and that leads to 26. Bc4 because 26...dxc4 allows 27. Rd8 and it is officially international day of happiness.

Black to move 30:

click for larger view

A. 26...dxc4? 27.Rd8!
B. 26...Qf7/Qc6 27.Qxb4 Qxc7 28.Bxd5+ Nxd5
29.Rxd5

click for larger view

white is ahead by a passed pawn.

click for larger view

and suddenly the mill needs more grease than grist!

After 26.Bc4 Qf7, also 27.Rhe1 seems to do the trick!

click for larger view

26.Bc4!

Pinning the d pawn in two ways and creating a primary threat of Bxd5, clearing the obstruction for Rd1. Black has no satisfactory defense:

A) 26... dxc4 27.Rd8 Re6 (Rxd8? 28.cxd8=Q) 28.Rhd1 Kf7 29.Rxe8 R6xe8 30.Rd8 poses no problems for white.

B) 26... Qc6 (to protect d5) 27.Qb6! Qxb6 28.cxb6 Rxb6 29.Rxd5!! (the secondary threat) Nxd5 (Rc8|Rc6 30.Rd8#!) 30.Bxd5+ Kf8 31.Bxa8 and black can't stop 32.c8=Q

B.1) 27... Rc8 28.Qxc6 Rxc6 29.Rxd5! Nxd5 (R6xc7 or Rxc5 30.Rd8#) 30.Bxd5+ Kf8 31.Bxc6 Rxc7 32.Be4 with a won endgame.

B.2) 27... dxc4 28.Rd8+ Kf7 (Rxd8 29.cxd8=Q) 29.Rxa8 Qxa8 30.Qb8 wins.

C) 26... Qe6 27.Rxd5! Nxd5 28.Rd1 Qf5+ 29.Ka1 Rc8 30.Bxd5+ Kf8 31.Be4 Qe6 32.Qb6 Qxb6 33.cxb6 Rxb6 34.Rd8+ wins

D) 26... Rc6 27.Bxd5 Nxd5 28.Rxd5 Qg6+ 29.Ka1 and black can't stop 30.Rd8.

Instead, the natural 17...Nxf6 = gives Black a perfectly playable game and avoids the complication leading to 26. Bc4! .

My failed solution 26. Qxb4 fizzles out to equality after 26. Qxb4 Rc8, as play might continue 27. Bd3 Rf6 28. Rhe1 Rxc7 29. Bc2 Qe7 30. Bb3 Rxc5 31. Qb8+ Rf8 32. Qxe5 Qxe5 33. Rxe5 g6 34. Bxd5+ Nxd5 35. Rexd5 Rxd5 36. Rxd5 Rxf3 37. a4 Rf6 = (Fritz 14).

Here's my breakout of the winning combination:

<26. Bc4!> The simple point of this pin tactic is that 26...dxc4? loses on the spot to 27. Rd8! with a decisive pin on the Black Queen. The more subtle point is that it overloads and puts pressure on the critical d4 pawn, forcing a defense that exploits the back rank weakeness of the Black position.

<26...Qf7> Attacked twice and now defended twice. Ignoring the threat with 26...Kh8 costs more than a pawn, as after 27. Bxd5 Nxd5 28. Rxd5 the threat 29. Rd8 is decisive.

<27. c6> Putting more pressure on the critical d pawn, which is now attacked three times and defended twice.

Putting more pressure immediately on the d-pawn seems best to me.

However the computer doesn't like this move, and instead recommends 27. Rhe1 when Fritz 14 indicates play might continue 27...Rc8 28. Qxb4 Qxc7 29. Bxd5+ Nxd5 30. Rxd5 Qf7 31. Rdxe5 Rf8 (31... Qxf3 32. Qc4+ Kf8 33. Rf1 $18) 32. Re7 Qf5+ 33. Ka1 Qd5 34. f4 h5 35. a3 Rg2 36. R7e5 Qf7 37. c6 Rc2 38. Rc5 a5 39. Qxa5 Rf2 40. c7 Rc8 41. Qc3 Rxh2 42. Qg3 Rd2 43. Qh3 Qd7 44. Qb3+ Qf7 45. Re8+ Rxe8 46. c8=Q Rde2 47. Qxf7+ Kxf7 48. Qd7+ R8e7 49. Rf5+ Kg8 50. Qd8+ Re8 51. Qd5+ R8e6 52. Rxh5 .

<27... Rd6> Attacked three times and now defended three times, but at the cost of weakening the back rank.

<28. Qxa6> Exploits the back rank weakness, as 28...Rxa6 loses to 29. c8(Q)+ Qf8 30. Qxa6+ .

<28...Qe8> Perhaps this is not the strongest defense. Fritz 14 indicates Black can put up more resistance with 28... Qf5+! (diagram below)

click for larger view

Here white still wins after 29. Bd3!, as play might continue 29...Qf8 30. Qb7 Re6 31. Bc4! dxc4 32. Rd8 Rxd8 33. cxd8=Q Qxd8 34. c7 Qd3+ 35. Ka1 Re8 36. c8=Q Rxc8 37. Qxc8+ Kf7 38. Qb7+ Kf6 39. Qxb4 Qd4 40. Qf8+ Kg6 41. a4 Ne6 42. Qe8+ Kf6 43. Rc1 Qd5 44. Qb5 (+3.37 @ 20 depth, Fritz 14).

<29. Qb7 Qxc6 30. Qxc6 Rxc6 31. Rxd5 Rxc4>

If 31... Nxd5, then 32. Bxd5+ Kf8 33. Bxc6 decides.

click for larger view

Here, white can't play either 29 Ka1 or Kc1 as 29...Rxa6 is now playable because black's queen covers c8.

White has to play 29 Bd3, blocking his d rook in the process.

click for larger view

tickle c7 ground palms i remember thin d5 pick delve off or push c5 on among c6 and create a stack to be in use later riff i catch my drift c8 and cushion blow am c7 wait ok in ogle line match vow vociferous again debate the merit then inter glide favour any cause c6 ya pin create mayhem for black in lights camp i wag have then,

save tail d5 or grab e5 and trade away am route won c4 ash cant be taken pay camp nay sayer c6 future queen in make van path gap got page at c7 tan your honour cage bend to do ho oodles right of room dint bad c8 dibs,

rag churlish behaviour by black lets light in to seal the win tank f5 blink c6 at krypton c8 factor into the equation ave the point low oil and roil liquidate rook ash d8 final saviour jirk we see at e8 enact in evermore bus ash over believe e8 takes c6 why the point c6 in bag casher bet rook d5 or chest c6 erm both good to win sew in,

flag on cap it ok again ogle 5d from afar plans mind scud rides and c4 slides bishop fang tooth inch along edifice ogle 5d lag fallacy again gimme line chin do as a grim d5 marginal pin babel c6 tower crashes in grand bank job and got away scott free rock queen fakir sell padre cave and c4 over family thod d5 what else though in actual should be a draw f5 queen iron feint an e8 plus c6 why the point light bags up ply in route quad won i be proof c6 angles c7 thorn in side and c4 throat aims clink in fly dipoff aim dead try deem a flight in,

cad afraid foot d5 push on counter acts d5 an dangle padre act c4 good to get a plus carries c8 on if a promotion in air then welcome ive light pieces around queen a6 side an b7 command from late distanced rook eddy a wave in queen c6 gives up the ghost carrier d8 wins after trade away d5 and c4 impress d8 seals along a seventh and knight track e6 back pin ash c7 and double castle,

<BxChess: what if 30 Qxb4?>

The pawn on b4 is defenseless but the prosaic 26.Qxb4 would be probably met with 26... Rc6.

A more interesting idea is 26.Bc4, threatening 27.Bxd5+:

A) 27... dxc4 28.Rd8 winning decisive material.

B) 27... Qd7 28.c6 (28.Rxd5 Nxd5 29.Rd1 looks very good also)

B.1) 28... Qxc6 29.Rxd5 Qxc4 (due to 30.Rd8#; 29... Nxd5 30.Bxd5+ wins) 30.Rd8+ Kf7 31.Rc1 (31.Rxa8 Rc6) and the double threat 32.Rxa8 and 32.Rxc4 wins.

B.2) 28... Rxc6 29.Rxd5

B.2.a) 29... Nxd5 30.Bxd5+ (or 30.Qxd5+ Qxd5 31.Bxd5+ wins a piece) 30... Kf8 (30... Re6 31.Bxa8 wins a piece at least) 31.Bxc6 Qxc6 32.Rc1 looks winning.

B.2.b) 29... Qf5+ 30.Ka1 Rxc4 31.Rd8+ Kf7 32.Rxa8 with an exchange ahead, seems to win.

C) 27... Rg2 28.Bxd5+ Nxd5 29.Rxd5 Qg6+ 30.Ka1 (30.Kc1 Qc2#) 30... Rg1+ 31.Rd1

C.1) 31... Rxd1+ 32.Rxd1 Qc2 33.Rd8+ Kf7 34.a3 (34.Rxa8 Qc1#) 34... b3 35.Qd2 Qxd2 (35... Qxc5 36.Rxa8 wins) 36.Rxd2 with a won ending. For example, 36... Ke7 37.c6 followed by Rd7, tying the black king and rook.

A quick engine run suggest Rhe1 as better than c6. Also (as already pointed out by <Jim>) 28 ... Qf5+, and B would still be in the game. After ... Qe8 it is heading towards 1-0

me, above: 30...Qxb4 31 cxb4 Rf8 32 Rd8 Rc6 wins.>

It seems that my previous post is correct, but woefully incomplete.

1) White can continue 33 Rd7, and, because of 33...Rc8?? 34 Rd8+ Black cannot immediately win the c-pawn. In fact, White can save a valuable tempo by playing 32 Rd7 directly, so let's show the position after <32 Rd7>

click for larger view

Black to play and win.

2) Black plays 32...Rc6 and threatens to win the c-pawn by 33...h6, 34...Kh7 (answering Rd8? with ...Rg8) and 35...Rc8 since 36 Rd8 is no longer check.

3) White can counter this by racing his Q-side pawns forward in time to save the c-pawn.

4) Black counters this by capturing the f-pawn, threatening to mate the White King with his two Rooks (see variation [A]), or simply advance his K-side majority.

5) White can and must therefore force Black to give up a Rook for the q-side pawns.

6) Black is left with a 2 Pawn advantage that seems to be a book win. Here are the main variations, found with the help of Crafty EGT:

<26 Rxd5 Nxd5 27 Bc4 Qf7 28 Rd1 Nc3+ 29 bxc3 Qxc4 30 Qxb4 Qxb4 31 cxb4 Rf8 32 Rd7> (see diagram, above) <32...Rc6 33 Kc2 (or [A]) 33...Rxf3 34 Kd2 h5 35 a4 Kh7 35 a5 ab 36 ab Rxc5 37 b6 Rb3 38 Rd8> If 36 Rd6 Black just advances his pawns. <38...Rxb6 39 c8Q Rxc8 40 Rxc8 Rb2+> and wins. (Even without the check, e.g., after 34 Kd1, this is still winning.) R+gP+hP v. R is a tablebase win, although a surprisingly difficult one.

<[A] 33 a4 Rxf3 34 b5> (34 Kc2 transposes back to the main line) <34...ab 35 ab Rxc5 36 Rd8+> (36 b6? Rb3+ 37 Ka2 Rxb6 38 Rd8+ Kf7 39 c8Q Ra5#) <36...Kf7 37 c8Q Rb3+ 38 Ka2 Rxc8 39 Rxc8 Rxb5>, and with the White King cut off, this looks like a fairly straightforward win for Black.

There are some additional variations and subtleties, but they don't seem to change anything.

Here are some Crafty EGT links I used: http://www.chessvideos.tv/endgame-t... and http://www.chessvideos.tv/endgame-t... and, of course, the tablebase http://www.k4it.de/index.php?topic=...