After 50 games Stockfish leads 15-9 with 26 draws. Stockfish won two more game pairs, it has a comfortable lead at the half way point of the match. There were two more pairs with two white wins.
Games 41-42 started with an 18-ply sideline in the Alekhine defense, modern Flohr variation. The engines exchanged a pair of minor pieces and opened the d file, the black king was still in the center. In game 41 both engines developed their pieces and Stockfish castled. There was a pawn exchange on the king side, then Stockfish gave a pawn on the queen side and exchanged a pair of knights. Stockfish's eval came down, it created a passer in the center through a bishop exchange. The game reached a RRB vs RRN position, Leela also created a passer but its eval came down and the engines shuffled. The engines traded pawns, the game was adjudicated after a pair of rooks was exchanged.
In game 42 the engines repeated game 41 for 19 plys with a transposition. Stockfish's eval started to increase, there was a pawn exchange on the king side like before and Stockfish pushed pawns on the king side. Leela's eval increased as well, on the queen side there was a series of exchanges that opened files and most minor pieces were gone.
Stockfish moved a rook to the back rank and forced the black king forward. The white major pieces moved to the e file attacking the knight on e7. Stockfish gave a pawn on the king side and its king found safety behind a black pawn. It gave another pawn and exposed the black king, seeing a win in its PV.
Stockfish traded RR for QN, it captured two pawns and the white king moved forward. Leela lost more material and the game ended in a tablebase win. Stockfish wins the game pair, it leads 12-7.
Games 43-44 started with a 22-ply line in the Catalan open defense. There was a Q vs RB imbalance with black a pawn up and the black king was still uncastled. In game 43 Leela regained the pawn and Stockfish castled its king. Evals increased as the engines shuffled for a while, on move 26 there was a series of exchanges and the engines reduced to a Q vs RB position.
The engines exchanged a pair of pawns on the king side and the white king moved forward. Stockfish pushed the e pawn and it became a passer. Leela attacked the black king with its queen, it pinned and captured the bishop.
The white queen blocked the black passer, Stockfish protected it with its rook. The black king supported its queen side pawn, this let Leela use its pawn majority on the king side to create a passer. The game ended in a tablebase win.
In game 44 Stockfish regained the pawn and Leela castled its king as in game 43. Evals increased steadily, the engines exchanged knights, there were pawn moves but no exchanges. On move 40 Stockfish gave a rook for a bishop and pawn, then captured another pawn and the game reached a Q vs RR position with white two pawns up.
Stockfish exchanged pawns and created a passer in the center, then it captured a pawn and created connected passers on the queen side. The white king moved forward on the king side and captured another pawn, Stockfish saw the win in its PV. The engines cleared the king side pawns completely, there were 3 white pawns left. Stockfish pushed a passer to the 7th rank, Leela lost material and the game ended in a tablebase win. There were two white wins in this pair, Stockfish leads 13-8.
Games 45-46 started with a sideline of the Sicilian, Scheveningen, Keres attack variation. There was one pair of pawns exchanged and all pieces were on the board. In game 45 Leela pushed pawns on the king side, the engines castled in opposite directions. The engines exchanged pieces on the queen side and evals came down. Stockfish pushed the d pawn and it became a passer, the engines locked both the king side and the queen side. The game reached a RRB vs RRB position, Leela captured the black passer and exchanged a pair of rooks. The game was adjudicated when evals were low enough for the draw rule.
In game 46 Stockfish pushed pawns on the king side but the engines didn't castle right away. Stockfish's eval increased, it exchanged minor pieces on the queen side and blocked the center with a knight. On move 17 Leela thought for 17 minutes and its eval jumped, both engines castled long as Stockfish threatened to open the king side. There was a pawn exchange the weakened the center, Stockfish had two bishops aiming at the black king and the pieces around it.
Stockfish exchanged knights and opened the d file. The black king moved to b8 to get away but that led to a discovered queen skewer. Stockfish gave a rook for a bishop, then a series of exchanges reduce to a queen ending with white two pawns up.
Stockfish had a passer on the 7th rank, Leela used checks and repetition to capture the passer. Now Stockfish used checks to get its king forward while keeping its pawns safe. The white king side pawns moved forward and Stockfish created another passer on the 7th rank. The queens were exchanged and the game ended in a tablebase win. Stockfish wins the game pair, it leads 14-8.
Games 47-48 started with the French Winawer, advance variation played in high level human chess. In game 47 Stockfish pushed pawns on the queen side, then exchanged pawns and knights in the center. Stockfish captured a pawn and exchanged minors on the king side, opening the h file for the white king side rook. Leela castled long and Stockfish moved its king without castling. On move 20 Stockfish thought for 31 minutes and its eval jumped, though Leela's eval stayed around 1. Leela developed the rook through the h file and moved it to the center, doubling rooks on the d file. A pawn exchange opened the h file and Leela regained the pawn and opened the d file. Leela captured another pawn, the black king was starting to feel trapped with major white pieces threatening it from both sides.
Stockfish regained the pawn and opened the g file, it kept the d file blocked with a rook. Leela moved its major pieces to the f file and Stockfish had to defend the f7 pawn as well. The black king became more exposed, on move 57 Leela exchanged rooks and reduced to a QRB vs QRN position.
Leela threatened mate and captured two pawns, then it drove the black king forward on the queen side. Stockfish lost material and the game ended in a tablebase win.
In game 48 Stockfish thought for 41 minutes on its first move, and then Leela played a move that wasn't in its PV. The engines exchanged pawns in the center, then in a long PV agreement Stockfish gave a knight for two pawns and opened the d file. The black king moved without castling and Stockfish castled long. Stockfish gave a rook for a bishop, its attack on the black king compensated for the lost material. The black king ran forward to the queen side, Stockfish gained material and the game reached a RBN vs RRN position with white two pawns up.
Stockfish's eval increased while Leela's eval was stable for a long time. Stockfish captured the e pawn and the engines exchanged knights. Leela moved its rooks forward and captured a pawn back on the king side. Leela gave a pawn to break the white pawn structure on the queen side, Stockfish pushed a passer to a6 where it was protected by the bishop. The white king moved forward, after move 54 Leela's eval started to react. On move 61 a pair of rooks was exchanged.
Stockfish pushed the c passer forward and Leela couldn't stop the two white passers. Stockfish queened twice and mated. There were two white wins in this pair, Stockfish leads 15-9.
Games 49-50 started with an 18-ply sideline of the KID orthodox variation played in human chess. The center was locked, both kings castled and all pieces and pawns were on the board. In game 49 the engines pushed pawns on the king side, a pawn exchange opened the e file and both engines created a passer on the f file. Evals came down quickly, the engines exchanged minor pieces and a pair of rooks, then Leela gave a rook for a bishop and its passer moved to the e file. The exchanges continued and the game was adjudicated on move 41. In game 50 the engines exchanged a pair of pawns in the center, then Stockfish pushed pawns on the queen side and opened the a file. Evals came down as the engines exchanged minor pieces and a pair of rooks, the game reached a QRN vs QRN position. Stockfish opened the h file and the game was adjudicated after the engines exchanged rooks.
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