Sunday, June 28, 2020

Season 18 superfinal games 41-50

After 50 games Stockfish leads 10-8 with 32 draws. Leela got within 1 point twice, and Stockfish won the reverse game in both game pairs. At the halfway point of the match Stockfish keeps a 2 point lead, still quite close and anything can happen. 

Games 41-42 started with a Scotch game modern defense variant, the black queen came forward and the black king moved and could not castle. In game 41 there were many early exchanges and only QRB vs QRB remained on move 18.

Evals slowly increased, Leela was a pawn down but had a better pawn structure, especially on the king side where Stockfish had doubled pawns. The engines exchanged queens and Leela managed to capture all the black pawns on the king side. 

Leela was careful and patient with its king side pawns, after 15 moves Stockfish decided to give its bishop and remove them. Leela had enough pawns left to win a RB vs R ending.

The pieces stayed on the board a bit longer in game 42. After exchanging queens Stockfish had a bishop pair, Leela went a pawn up but Stockfish's eval started to increase. Stockfish traded a bishop for a knight and only RRB vs RRN remained on move 27, Stockfish's eval was over 2.

Stockfish captured a pawn on the king side and created a 3 to 1 pawn majority. The engines exchanged pawns and Leela created 2 passers on the queen side. It pushed a pawn to the 2nd rank and its low eval showed it thought it was relatively safe. Stockfish's eval continued to increase, it controlled the 7th rank with a rook and it was sure it was going to win.

Leela couldn't hold on to the d pawn after the white king moved towards it. The other black passer was too far to be a serious threat, Stockfish doubled rooks on the 7th rank and Leela realized it was going to lose.

Leela avoided an immediate mate but Stockfish captured the knight a few moves later. The game was adjudicated in a RB vs R position with one white pawn to ensure the win. There were two white wins in this opening, lead is still +2.

Game 43 reached a R vs NN imbalance early. Leela was two pawns up, the engines exchanged queens and a pair of rooks and the game reached a RB vs BBN position on move 32. Stockfish's eval came down to 0, the most Leela could do was to give a pawn a get a passer to the 7th rank. Leela continued to play, the game was adjudicated in a R vs BN position on move 78. In game 44 Leela pushed pawns in the center and planted a knight on the 3rd rank. Stockfish exchanged a bishop for the knight and cleared the black central pawns. After a series of exchanges the game reached a RN vs RN position on move 35. Both engines had a pawn near promotion, after a while they traded knights and captured the passers leading to a drawn rook ending. 

In game 45 Leela pushed pawns in the center and Stockfish pushed pawns on the queen side. Evals mostly stayed below 1, Leela waited until move 20 to castle though its king had low pawn cover. Leela surprised Stockfish on move 23 with a pawn move to f5. The white king side completely opened, and then Leela gave a pawn and created an advanced passer in the center. Stockfish's eval jumped over 2, a series of exchanges led to a RBN vs RBN position.

The black knight was almost trapped, Stockfish lost two pawns to save it. While Stockfish concentrated on getting rid of the passer Leela captured another pawn, it was two pawns up in a RN vs RB position on move 49.

Leela drove the black king back and captured another pawn, the game was adjudicated soon after that.

In game 46 Stockfish pushed pawns on the king side and castled short like the previous game. There were several early minor piece exchanges and queens were also off the board. Stockfish's eval started to increase after Leela grabbed a pawn on the queen side and allowed Stockfish to create a pawn majority on the king side. The white king moved forward supporting its pawns and Stockfish placed a bishop and pawn pair deep in black territory. After exchanging a pair of rooks the game reached a RBN vs RBB position and Stockfish went two pawns up.

The black bishop pair was strong, Stockfish's passer could not advance and it was not clear how Stockfish can win, though its eval continued to increase. On move 50 Stockfish traded its knight for a black bishop, then traded rooks and gave its passer to take the black h pawn.

The result was an opposite color bishop ending. Usually a 2 pawn advantage is not sufficient in such an position but this was an exception. The connected pawns needed the attention of both black king and bishop, and by the time Leela captured one pawn Stockfish pushed the c pawn to the 6th rank. Leela could not stop both white passers and Stockfish promoted one to a queen, winning the game. There were two white wins in this opening, lead is still +2.

Leela opened the king side and castled long in game 47. Stockfish exchanged queens and opened the queen side, its eval dropping to 0 though Leela was a pawn up. Only rooks and bishops remained on move 29, both kings were exposed to checks. Leela avoided a repetition draw but the draw rule adjudicated the game. Game 48 started with a similar setup with Stockfish castling long. The white queen came forward and Stockfish tried a king side attack. Leela defended well, it tried to exchange queens but Stockfish refused. After several attempts there was a series of exchanges instead and the game reached a QN vs QB position on move 35. Evals were low, the game continued for 35 moves and was adjudicated when the pawns stopped moving.

Black had an advantage from the opening in games 49-50. In game 49 all the bishops were exchanged by move 16, with all pawns still on the board. Leela didn't castle its king, instead the king walked to the king side. Stockfish's eval came down and it mostly played waiting moves. The engines opened a file on the queen side and exchanged a pair of rooks, after that the game was adjudicated by the draw rule. In game 50 Stockfish castled early and the engines exchanged pawns with all pieces on the board. Leela didn't castle as black, starting from move 21 the engines exchanged pieces and on move 29 only RB vs RB were left with Stockfish a pawn up. The engines mostly shuffled with some pawn moves or captures, Leela slowly lowered its eval. The game was finally adjudicated on move 103, close to a 50 move draw. 

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