Saturday, June 27, 2020

Season 18 superfinal games 31-40

After 40 games Stockfish leads 8-6 with 26 draws. Only one decisive game, Leela wins a game pair and Stockfish's lead is +2. The match is not so one-sided as it was in the first 10 games, Leela is still fighting.

A long series of early exchanges left only RRB vs RRB on move 21 in game 31. The engines stabilized the pawns and then exchanged a pair of rooks. A second series of exchanges reduced to an opposite color bishop ending, Leela had connected passers and Stockfish had a passer that reached the 2nd rank. Leela thought it had an advantage, it took a long time for it to lower its eval for the draw rule on move 96. The pieces stayed on the board longer in game 32, the engines cleared the queen side pawns and exchanged queens and minor pieces. Evals came down to 0 and the game was adjudicated when the pawns stopped moving.

The center opened early in game 33 and the engines exchanged most pieces. Evals climbed over 1.5, on move 25 only BB vs R remained. Stockfish was a pawn up but it had two weak pawns on the queen side and only one piece to defend them. 

The bishop pair was very strong, Stockfish played passively and tried to protect its pawns. Leela's king came forward targeting the black a pawn. There was no room for the rook and king as defenders and Stockfish lost the a pawn on move 46.

The black rook became active again, but it couldn't attack on its own and the white pawns were protected. Leela slowly pushed the a pawn forward, with its king and bishops supporting. The game was adjudicated when the white king found a way to move behind the black pawns.

In game 34 the black queen came forward early, Leela traded it for two bishops and a knight. Stockfish captured two pawns and its eval went over 2 and kept increasing. Both engines attacked and the position became chaotic, Stockfish threatened mate on the king side while Leela pushed two pawns on the queen side facing the white king. After material sacrifices from both engines the game settled down in a Q vs RN endgame on move 39. 

Despite the high eval Stockfish could not find a way to win here. Leela abandoned the a pawn and placed its rook on the 6th rank. Together the rook and knight controlled the d6 square, stopping the white pawn. Stockfish got nowhere with its queen alone and it gave up trying as the 50 move draw approached. Leela wins a game pair and Stockfish's lead is +2.

Leela pushed pawns on the queen side in game 35, despite castling long. A file opened in the center and the engines exchanged queens and a pair of bishops. Evals were low and the engines started to shuffle. There were a few more piece exchanges and pawn moves, the game was adjudicated when Leela lowered its eval for the draw rule. In game 36 Stockfish castled short and Leela pushed a pawn to h3. Stockfish went a pawn up, its eval peaked at 1.5 and then came back down. The engines cleared most of the pawns on the queen side, then shuffled for a while. Evals were close to 0 and the game was adjudicated on move 35, in a position with many pieces and pawns on the board. Too soon?

Leela pushed a pawn to h6 in game 37, and Stockfish castled short nevertheless. The engines exchanged queens and all bishops, that made the black king safe. After exchanging a pair of pawns the engines started to shuffle on move 35. Evals were around 1 but neither engine moved a pawn and the game ended in a 50-move draw. Game 38 started similarly with a white pawn on h6 and Leela castling short. Stockfish attacked the king side, capturing two pawns and making its h pawn a passer. Leela hid its king behind the passer and exchanged queens. Leela avoided opening a file on the king side and exchanged bishops, its king was trapped in the corner but somehow safe. Evals came down and the game was adjudicated in a RRN vs RRN position, Leela's PV showed a drawn double rook ending.

In game 39 Leela pushed pawns on the king side and its king stayed uncastled in the center. Stockfish opened a file on the king side and gave a rook for a bishop. The white king was exposed and Leela quickly exchanged queens, Stockfish's eval came down to 0. The game reached a RRN vs RBN position, and the engines gradually exchanged pawns until none were left. The material advantage was not enough for a win, Leela was slow to lower its eval and the game was adjudicated on move 90. In game 40 again Stockfish pushed pawns on the king side, it did castle its king but without pawns the king was still exposed. Leela gave two pawns and opened a file in the center, its eval turned negative after it doubled rooks in the file. Leela went on the attack with many threats and pins, however Stockfish's eval was at 0. After most pieces were exchanged the game reached a RB vs Q position with white two pawns up. Leela could only give checks, after 25 moves it lowered its eval for the draw rule.

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