Wednesday, May 15, 2019

Season 15 superfinal, games 11-20

After 20 games Leela leads 3-1 with 16 draws. Stockfish equalized after a Leela blunder in an endgame. Leela responded with two wins. So far only Leela has shown it can turn an advantage to a win. It is still early in the match but Stockfish does not appear to be strong enough to win.

Games 11-12 started with a 17-ply book in the French Tarrasch closed variation. Evals fell to 0 very quickly in game 11, the engines gradually exchanged pieces and Leela's eval turned slightly negative. On move 30 Stockfish gave a rook for a knight and pawn, Leela refused to exchange queens and the game reached a QRB vs QRR position. The engines captured pawns, then in a series of exchages reduced to a B vs R drawn ending.

In game 12 Stockfish's eval fell to 0 very quickly, Leela kept a small eval that stayed under 1. On move 32 Leela captured a rook for a knight, Stockfish had a passer it pushed to the 3rd rank. The game reached a QRB vs QBN position, the engines shuffled and Leela's eval slowly came down. On move 62 the queens were exchanged and Stockfish created a second advanced passer. The game was heading for a draw when suddenly Stockfish's eval jumped over 4.

Leela should have blocked the d pawn with its rook. Instead Leela had to block with the king, it couldn't take the pawn because it would lose the rook in a fork. It took Leela 6 moves to realize it was losing. The two passers were too strong and Leela couldn't stop both without losing material.

Games 13-14 started with a 22-ply book, a popular Symmetrical English variation. In game 13 Stockfish had an eval of around 1. It opened the king side but did not develop an attack on the black king. Leela opened a file on the queen side, the engines exchanged a pair of rooks and evals came down. The engines exchanged pieces until the game was adjudicated in a QBN vs QBN position. In game 14 Leela pushed pawns on the king side, Stockfish gave a bishop and cleared the white king side pawns, exposing the white king. The engines continued to exchange pieces and pawns and evals came down. On move 43 only RN vs R were left, Leela continued to play another 30 moves but Stockfish held the draw.

Game 15 started with a network crash and was restarted. Stockfish had an eval over 1 from the start, it kept its king in the center even though the engines cleared the center pawns. The black queen was very active, Leela went a pawn up. By the time Stockfish moved its king to safety evals came down. Stockfish regained the pawn, after queens were exchanged the position became very drawish with pawns only on the king side. The game ended in a tablebase draw.

Leela started game 16 with an eval over 1 that increased slowly. All the pawns remained on the board, the engines mostly played behind the pawn lines. On move 21 Stockfish remained without a knight, a disadvantage in a closed position. Stockfish's eval was under 1, only when Leela's eval reached over 3 did Stockfish start to think it was in trouble.

The black king side rook was trapped, and the c6 pawn was a long term weakness which Leela could attack with multiple pieces. The engines shuffled for a while, then Leela found a plan to improve its position. The doubled pawns on the d file had to be protected, Leela moved its king to the center so it could take the role of defender.

Leela could attack more freely with its pieces, it captured the h4 pawn, the first pawn to be taken in the game. A few moves later the queens were exchanged leaving only RRN vs RRB, Leela's eval was winning, Stockfish still wasn't convinced. Indeed, there was a very long shuffle, only on move 120 Leela went two pawns up. Stockfish finally agreed it was losing, the game was adjudicated on move 143.

Games 17-18 started with a 22-ply book in the King's Indian defense, Bayonet attack. Evals were over 1 from the start of game 17, the center was blocked and Stockfish had a significant space advantage on the queen side. Stockfish gave a pawn and opened the queen side, then moved its knights forward. Leela had two connected passers on the queen side while Stockfish put a protected knight on e6. Leela gave a rook to get rid of the white knight, simplifying the position. After some shuffling Stockfish gave the material back and captured the black passers. The engines reduced to a BB vs BN position, Stockifsh was a pawn up but could only shuffle. The game was adjudicated on move 111 with the 50-move draw getting close.

In game 18 Stockfish pushed pawns on the king side and opened a file, while Leela pushed pawns on the queen side all the way to a6. Leela's eval was over 2 after it opened a file on the queen side and exchanged several pieces. Stockfish's eval also increased slowly, it had less space and its pieces surrounded the black king defensively, trying to hold the position.

Leela applied pressure and tried to find a way to break black's position. After exchanging the LS bishops Leela gave a pawn temporarily and forced a queen exchange. Evals jumped over 5 as Stockfish's defense collapsed.

All the black pawns were on dark squares, targets for Leela's bishop. Stocksih couldn't protect them all and Leela went two pawns up. Then it was just a matter of pushing pawns forward to get the win.

In game 19 Stockfish castled long while Leela kept its king uncastled and pushed pawns on the queen side. Evals came down to 0 by move 20 and stayed there for the rest of the game. Leela pushed a pawn to a3 but could do no more on the queen side. Stockfish opened the king side but did not attack the black king. The engines continued to exchange pieces, Stockfish ended the game with perpetual check. In the reverse game 20 both engines castled long. There were many early exchanges, with RN vs RB remaining on move 25. The game reached a N vs B ending which continued for more than 50 moves before reaching a tablebase draw.

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