Season 13 premier division after RR1

Crosstable after RR1



Stockfish is leading the table with a +3 score and no loss, including a win against Komodo. Komodo is the only other engine with a positive score of +1. Houdini is the only other engine with no loss, it drew all the games in the RR.
Chiron is last with a score of -2, there is a good chance it will be relegated back to division 1. Ethereal has a 0 score so far, two wins (one against Fire) and two losses. It is quite possible it will survive this division.
Some of the openings were biased and it should be interesting to see the results of the reverse games in the next RR.


A few interesting games

Andscacs - Ginkgo: Andscacs pressed hard in the opening game. Its eval peaked over 1.5 despite being down an exchange. Ginkgo managed to stop connected passers, one on the 7th rank, in a QB vs QR position. The game ended in a draw.

Ethereal - Fire: Ethereal came out of the opening a pawn down but with an advanced passer in the center and increasing evals. Ethereal exchanged pieces, giving a rook for a bishop as well. The game reached a BB vs RB position, Ethereal 3 pawns up. Fire traded the rook to force an opposite color bishop ending, still Ethereal found the win. Ethereal with a win in its opening game, how far can it go in the premier division?

Stockfish - Komodo: Featured game, see below. 

Ginkgo - Komodo: Komodo gave a bishop for two pawns early in the game. Ginkgo's king was exposed, Komodo did not attack and the engines shuffled for 20 moves. It seemed Ginkgo lost its patience, the position opened up and the engines exchanged queens, with evals increasing in favor of Komodo. Ginkgo's position collapsed, the game was adjudicated after Komodo won a piece and was 3 pawns up.

Fire - Chiron: Chiron moved its queen forward and Fire almost trapped it. By the time the queen found safety Fire attacked the back rank and black king with its rooks and queen. Fire won a bishop and the RN vs R ending was won for white.

Andscacs - Ethereal: Ethereal's 24th move led to a long series of exchanges and a RB vs RN position on move 36. Andscacs was two pawns up with eval over 1.5 and increasing. Ethereal tried to hold against two white passers, it managed to capture one but allowed Andscacs' rook to move forward and attack the black king. Andscacs found a way to exchange rooks and advance its king, winning the B vs N endgame.

Fire - Komodo: Fire was up a rook for a knight in a closed position. The engines shuffled for a very long time, both had very little time when Fire played several inaccuracies after move 98. The game reached a RRB vs RBN position with a pawn wall across the board. Only the black pieces could move freely, Komodo patiently maneuvered until it captured two pawns. Fire's position collapsed and the game was adjudicated.

Andscacs - Stockfish: Andscacs thought it was ahead when Stockfish's eval turned negative on move 31. The engines castled in opposite directions, Stockfish opened a file on the queen side with doubled rooks facing the white king. Andscacs traded Q for RB and the game reached a RBN vs QN position. It took Stockfish another 30 moves to win but there was never doubt it would.

Ethereal - Chiron: The engines castled in opposite directions, Ethereal pushed pawns on the king side towards the black king. Chiron exchanged pieces and gave a knight for pawns to open the queen side and counterattack. The game reached a RRB vs RR position, Chiron's king was trapped in the corner and the engines started to capture pawns. The game was adjudicated just before Chiron lost its last pawn.

Stockfish - Ethereal: The engines shuffled in an closed position and didn't seem to make progress. On move 45 Stockfish saw an opportunity and pushed pawns on the king side. After a long series of exchanges the game reached a RN vs R position, Stockfish converted the win without difficulty.

Komodo - Chiron: Komodo started a king side attack with a bishop sacrifice. After almost all pieces were exchanged Komodo was two pawns up in an opposite color bishop ending. Chiron held the draw but it took more than 200 moves before the evals were low enough to adjudicate. 

Featured game: Stockfish - Komodo
Premier division, round 1
Link to game on TCEC

Stockfish's eval was over 1 after book, Komodo's eval remained mostly under 0.5. Stockfish gave a pawn to open the queen side. The position was unstable, with Komodo threatening a fork with one knight, Stockfish threatening to take the other knight, the b4 pawn pinned and rooks facing each other on the d file.

There was a series of exchanges that resolved the tension. Stockfish was ahead by a knight for 2 pawns and Komodo had connected passers on the queen side. Evals increased very slowly, Stockfish's eval was close to 2 while Komodo's was still under 1. There was a long PV agreement and it wasn't clear whether Stockfish could convert.

The engines followed the PV line and the game reached a QBN vs QB position on move 33. The pieces moved around and evals did not change a lot, on move 44 Stockfish exchanged queens.


Evals were almost constant for a very long time, and the endgame was very slow. Stockfish's bishop made sure the queen side pawns did not advance. In the end Stockfish moved its king forward and this broke Komodo's defense. Can Stockfish hold the reverse game?

Season 13 division 1 final results

Final crosstable


Ethereal and Chiron promote to the premier division, Booot and ChessBrain are relegated to division 2.

Promotion of Ethereal and Chiron was never in question, they both dominated the division from the start. Fizbo lost touch with the leaders in the second half of the division, it lost three games, including a loss to Ethereal and to Chiron.

The relegation race was very close with 5 candidate engines. ChessBrain dropped to last place after a score of -5 in the second half of the division. Jonny with a score of +1 in the second half managed to climb out of the last place. Booot scored -1 and its only win of the division, it almost survived relegation. Its early crashes were its downfall, both because of the tiebreak and because of the lost points.

The premier division is about to start with Stockfish, Komodo, Houdini, Fire, Andscacs, Ginkgo, Ethereal and Chiron playing. This is the main event of the season where we get to see the really top chess engines competing, with long games and the highest level of chess. Stockfish is the clear favorite, the winner of the last two seasons. Houdini and Komodo are expected to compete for a place in the superfinal. Recall that last season Komodo won the premier league ahead of Stockfish, with Houdini only one point behind. It is unknown how well the other engines will play. Fire has been a constant 4th in the last seasons, Ethereal may also fight for 4th according to its author Andrew Grant. It is incredible that Ethereal started season 13 in division 3 and won three division in a row.

Good luck to all! 

A few interesting games

Chiron - Fritz: Fritz created a queen side passer early in the game. At first it appeared the black queen was in trouble, but it got away and Fritz connected its passer on the 3rd rank with a bishop. The game reached a RBB vs RBB position and evals gradually increased in favor of Fritz. The engines exchanged pieces and pawns, Chiron could not get rid of the black passer. In the end only bishops remained and the passer was good for a win for Fritz. A surprise loss for Chiron.

Fritz - Booot: Booot chose a RN vs Q imbalance early in the game, this turned out to be a bad idea. The black king was exposed, Chiron took over the 7th rank and together with a strong bishop pair threatened mate. The game was adjudicated before Booot lost its queen. Two Fritz wins in a row, it moves away from the relegation zone.

Jonny - Chiron: Jonny took a poisoned pawn with its queen early in the game. This quickly led to a R vs BN imbalance and negative evals around 3. It took Chiron close to 30 moves to get the win in a RN vs R endgame.

Ethereal - Fizbo: Ethereal created a central passer early in the game. A strong king side attack gave Ethereal a R vs B exchange advantage and evals over 2.5. Fizbo's compensation was the exposed white king, for a while Fizbo's eval came down below 1 while it made checks. Evals came back up and continued to increase when the white pieces sheltered the king and Ethereal had the initiative again.The game reached a RNB vs RB position and was adjudicated before the endgame was played out. This was the first loss for Fizbo in the division.

Chiron - ChessBrain: Chiron was a pawn up early in the game. The engines exchanged most of the pieces and only RN vs RB remained on move 23. Chiron created a queen side passer and reduced to a winning rook ending.

Fizbo - Fritz: Fizbo trapped a black rook and went up R vs N exchange. Fritz tried to counter with a queen side passer, Fizbo made sure it won't advance. Fizbo created a passer in the center and then exchanged down to a RB vs BB position. The white passer was worth a piece and it gave Fizbo the win.

Jonny - Laser: See my live blog of the game. Jonny had a R vs B exchange advantage and the game reached a RRB vs RBB position on move 30. Jonny controlled the 7th rank and after exchanging a pair of rooks it managed to get a winning endgame. Jonny's win complicated the bottom of the table.

Ethereal - Chiron: See featured game below. Ethereal wins and evens the head to head score against Chiron.

Laser - ChessBrain: Laser had an eval over 2 when the position opened up in a RRB vs RRN position. The game reached a rook ending with Laser a pawn up. ChessBrain did not have tablebase access and didn't realize it was lost until the game reached a tablebase adjudication.

ChessBrain - Fritz: ChessBrain went up a pawn early in the game. After some shuffling the engines exchanged pieces until only B vs N remained, Fritz had to block the white passer on the queen side and ChessBrain found a zugzwang win.

Ethereal - Laser: Laser got into trouble very early. Ethereal didn't castle, instead it launched a deadly king side attack. Evals shot up quickly, Laser exchanged most pieces and lost only a little material. The game reached a R vs B position, and an easy win for Ethereal.

Fritz - Ethereal: Evals were stable and close to 0 until Fritz decided to sacrifice a knight. It got 3 pawns in return and two passers, but evals became negative and increased slowly. Ethereal exchanged pieces until only BNN vs BB remained, then it captured the white passers with evals over 2. For a while it seemed Fritz might be able to hold a draw with its bishop pair, but then it blundered the game away.

Jonny - ChessBrain: Jonny won a pawn, then after some preparation exchanged down to a RB vs RB position. The endgame was very slow, Jonny captured a second pawn and had a king side passer. ChessBrain's lack of tablebase support was evident again, Jonny reduced to a winning 6-man position and ChessBrain thought it still had a chance.

After RR3 the standings are Ethereal +9, Chiron +5, Fizbo +1, Fritz -2, Jonny -3, ChessBrain -3, Laser -3, Booot -4. There are 5 engines fighting against relegation, Booot's crashes against ChessBrain and Fritz were very unfortunate.

Fizbo - ChessBrain: ChessBrain chose to open the king side, putting its king at risk. Fizbo was up a pawn with a bishop pair facing ChessBrain's knight pair, ChessBrain had an advanced passer in the center as compensation. The game reached a RBB vs RNN position, the bishops were very strong and the exposed black king was an easy target. ChessBrain lost a piece for pawns, Fizbo won the endgame.

Fritz - Chiron: Fritz had a small eval advantage for the first 50 moves, when the position opened evals became slightly negative but still close to 0. The game seemed to be heading for a draw, after a long shuffle Chiron took the initiative on move 80. It took a while but after most pieces were exchanged the game reached a RB vs Q ending. Chiron captured the remaining white pawns and reduced to a winning 6-man position.

Ethereal - ChessBrain: Ethereal gave a knight for 3 pawns. The game reached a RB vs RBN position and for a while it seemed ChessBrain can hold. On move 64 ChessBrain blundered and Ethereal's eval started to jump. It took Ethereal 20 more moves to reduce to a winning rook ending.

Only 4 rounds to go, the bottom of the table is Fritz -3, Jonny -3, Laser -3, Booot -4, ChessBrain -5. ChessBrain lost twice, but its remaining games are only against the other bottom 5 engines. All other contestants have at least one game to play against the top 3, Booot has to face all 3. Nothing is decided yet.

Fritz - Fizbo: Fritz was a pawn up early in the game, with an eval advantage that increased over 1. Fizbo gave a second pawn, opened the king side and threatened the white king. Fritz exchanged pieces and the game reached a QBN vs QR position. Evals slowly came down, then shot up over 2 after an unexpected Fizbo blunder. Fritz drove the black king out of the corner and captured a pawn, evals slowly increased until the game was adjudicated. An unexpected win for Fritz. 

Booot - ChessBrain: The engines castled in opposite directions, ChessBrain gave a pawn to open the queen side and tried to attack the white king. After a series of exchanges the game reached a RN vs Q imbalance, Booot 2 pawns up and evals over 1. ChessBrain's attack on the white king was not strong enough, a white passer forced ChessBrain to lose a piece. Booot's material advantage was enough for a win. This is Booot's first win of the division.

Fizbo - Chiron: The game started in a closed position. Chiron opened the king side and had much more space. It increased the pressure with the queen and a passer on the queen side and rooks on the king side. The game was adjudicated before Fizbo lost material. Two straight losses for Fizbo.

Now only 2 rounds to go, the bottom of the table is Fritz -2, Jonny -3, Laser -3, Booot -3, ChessBrain -6. ChessBrain is very close to being relegated back to division 2, Fritz and Booot improved their chances to survive.

Booot - Chiron: Booot had a small eval advantage from the opening, though Chiron had a queen side passer. Chiron took over after Booot gave a bishop for three pawns including the black passer. The game reached a R vs RB position, Chiron gradually captured and exchanged pawns. The game ended in a tablebase win for black. This loss means that Booot must win its last game to have a chance of surviving.

Fizbo - Booot: Fizbo had the advantage in a RRB vs RRB position, the game ended in a tablebase draw. Booot cannot survive, it will lose any tiebreak because of crashes.

Chiron - Laser: Chiron created a passer on the queen side. As the engines exchanged pieces the evals increased gradually, Chiron also had a bishop pair advantage. Eventually Laser lost a piece to get rid of the passer, the game reached a QBB vs QB position. It took Chiron a while, and perhaps Laser blundered but in the end Chiron found the win.

Ethereal - Fritz: Ethereal was a pawn down when suddenly its eval jumped over 3. Apparently Fritz ignored the danger to its king and was late in developing its queen side pieces, and it was slow to realize it was losing. Fritz gave a knight and exchanged pieces, its king was still vulnerable in a QRN vs QR position and the game was soon adjudicated.

Featured game: Ethereal - Chiron
Division 1, round 18
Link to game on TCEC

Evals were close to 0 with a small advantage to Ethereal. After the opening Ethereal had an isolated pawn in the center, Chiron moved its rook forward to apply pressure on it.



The rook immediately became a target. Ethereal could exchange it for a bishop but it made some preparations first. When the exchange was made Ethereal also had passers on the queen side. Evals were over 1 and increasing.


After exchanging queens the game reached a RBN vs BBN position. Chiron had an advanced passer but after Ethereal got rid of the black LS bishop Chiron lost control of the the queening square. 


Ethereal used attacks on the black king and pieces to advance its passer to the 7th rank and get a winning position.

Season 13 division 1 statistics

Draw rate, wins



Final draw rate was 62.5%.

Game termination

The three most common game termination causes were:
33.9% - TCEC draw rule
25% - TCEC win rule
24.1% - SyzygyTB

There were 2 crashes in the division.

Moves per game



Median= 55.3
Average= 61.1

There were only 7 games longer than 100 moves, the longest was 157 moves (Jonny - Laser, round 4, draw). 

Time per game (hours)



Median= 2:06
Average= 2:04

Openings

There were 2-move book openings in this stage chosen by Cato. Each opening was repeated 4 times in a round, and then again in the reverse games round. In total 14 2-move openings were used. The first letter of the ECO codes was distributed as follows:



If we use the opening 'family name' (using format FAMILY_NAME: VARIANT....) the top 3 are:
QGD - 16 times
Sicilian - 16 times
English - 11 times

The engines had a lot of freedom to choose the opening variant. Only 19.6% of the game pairs repeated the same ECO code twice, and 14.3% repeated the same opening variant. In 14.3% of the game pairs the ECO first letter was not repeated twice.

Reverse pairs, wins



Reverse pairs, same moves 

Pairs of reverse games diverged very quickly, 91.2% of the pairs diverged at most after 1 move. The longest repeated move sequence in a game pair was only 9 plys long. 

Season 13 live blogging, Thursday Aug 30th

Today we follow the Jonny - Laser game in round 18. Jonny is currently last with a score of -5, Laser is in 6th place with -2. Almost all of Jonny's losses have been to the two table leaders, and it has one win. If it wins this game it will have a better chance to survive this division. Laser also has only one win so far, it would like to get away from the relegation zone, and this is one of its best chances.

move 10: The engines followed a familiar line in the Sicilian Defense until move 9, where Laser chose an unpopular f5 move. The pawn exchange opened the black g file and both evals jumped. Is this a chance for Jonny?

move 15: The black king is uncastled in the center, trying to get away from the exposed king side. The white king castled long, it is also a little exposed but has some pawn support. Jonny's eval is over 1, always the optimist and not always trustable. Laser had a long 5 minutes think and its eval jumped over 0.7, maybe a real advantage?

move 19: There was a long PV agreement in which Jonny was a pawn down. However, Laser changed its mind on move 18. Its eval went down, Jonny responded with a jump to almost 2 and Laser's eval back over 1. Did Laser blunder? There is a longer PV agreement now showing a white passer on the 7th rank and a RRB vs RBB position.

move 24: BOOM, evals are jumping higher. There are going to be many exchanges in a forced line. Jonny is winning material, the rook cannot escape the pin and Laser can only exchange pieces and delay a little. Jonny seems to be heading for its second win.

move 30: The end of the forced line, now only RRB vs RBB left and Jonny has a pawn on the 7th rank, as was seen in the PV earlier. Jonny continues to be confident, though it probably won't be able to hold its a7 pawn. Laser has a bishop pair, I doubt it is strong enough to hold a draw.

move 38: Another long PV agreement, one pair of rooks is gone and so is the a7 pawn. Evals continue to increase slowly, the win for white seems inevitable.

move 44: A very long think by Jonny, and its eval jumped over 6.5. Laser is slowly getting there, eval over 5.5.

move 49: Game over.

Jonny closes the gap to Laser to only 0.5, there are now three engines in the race against relegation (Booot is the third). 

Season 13 division 1 after RR2

Crosstable after RR2



Chiron and Ethereal are tied at the top of the table, both seem to be on their way to qualify to the premier division. Fizbo in 3rd is the only engine without loss in the division, but it only has one win so far and it is two points behind the leaders.
The bottom of the table is more crowded. Jonny is last, it lost all its games against the leaders. Booot started the division with two crashes, but since it was limited to 16 threads it has been stable, drawing all its games except one loss. Laser, Fritz and ChessBrain are also very close to the relegation zone.

A few interesting games

Ethereal - Jonny: Ethereal had a strong knight pair which was better than Jonny's bishop pair in a closed position. Ethereal used the advantage to create a pair of connected passers in the center. Jonny's king was exposed in a QRN vs QRB position, Ethereal forced a queen exchange that led to a winning endgame.

Chiron - Fritz: Evals were close to 0 for the first 40 moves. The black king move forward on the king side where Chiron could attack it, This led to a simplification to a RB vs RN position with a pawn advantage for white. Chiron found a win after exchanging rooks.

Fizbo - Laser: Fizbo had an early pawn advantage on the queen side. Its eval was around 2 after clearing the center and exchanging pieces. After some shuffling the game reached a QRB vs QRN position. Laser was forced to give a rook for a bishop to remove one of the pawns and to avoid mate. The resulting endgame was winning for Fizbo.

Jonny - Chiron: Jonny played the opening badly and evals turned negative. Chiron opened files and pressed on the king side. Eventually Chiron managed to exchange pieces and reach a NN vs NN ending two pawns up. Two central passers were enough for a win.

ChessBrain - Ethereal: Ethereal started a king side attack with a knight sacrifice. After many exchanges and long forced lines only RR vs Q were left. Ethereal used its queen to attack the white king and capture pawns, ultimately winning though it took more than 25 moves.

Ethereal - Chiron: There were many early exchanges. Chiron went up a pawn and evals became negative, only RRN vs RRN were left on move 31. Chiron later gave the pawn back but gained two king side passers, Ethereal had to give a piece to stop them. The RN s R endgame was winning for Chiron. First loss for Ethereal in the season.

Fritz - Jonny: The game reached a RB vs BN closed position on move 64. Fritz broke through the queen side with a bishop sacrifice (after a Jonny blunder?). Jonny had to give its bishop to stop the passers and the R vs N endgame was a win for Fritz.

ChessBrain - Fritz: ChessBrain was a pawn down but up on eval. It blocked the center trapping the black rooks on the queen side, and attacked the king side. Fritz' king lost its supporting pawns and it was almost paralyzed. Fritz gave material to free itself, leading to a RN vs BB endgame,  ChessBrain two pawns up and winning.

Booot - Fizbo: After crashing twice Booot was reduced to 16 threads. Booot attacked on the king side, Fizbo defended and exchanged pieces. On move 31 RBN vs RRB remained, Booot two pawns up and with an advanced passer. It had a eval over 1.5 when it allowed Fizbo to trade pieces and pawns, leading to a draw.

Laser - Chiron: see featured game below. Chiron's first loss of the division.

Fritz - Ethereal: The center was blocked early in the game. Ethereal trapped the white king in the king side and then threatened to open the h file with a deadly attack. Fritz defended for a while but collapsed when Ethereal doubled rooks on the h file.

Jonny - ChessBrain: There were many early exchanges and only RRN vs RRN remained on move 21. Jonny's rooks controlled the central files, it had a pawn advantage on the king side with its king supporting the pawns. After exchanging a pair of rooks Jonny created a passer, and this led to a won rook ending. First win for Jonny in the division.

Jonny - Ethereal: Jonny grabbed a pawn and let Ethereal take the initiative and attack the exposed white king. An advanced black passer forced Jonny to trade its queen for RN, leading to a RBN vs QN position. Jonny was two pawns up but that was not enough against Ethereal's active queen. The game was adjudicated just as Ethereal was about to capture more white pawns leading to a clear win.

Chiron - Jonny: Jonny grabbed a pawn (again), allowing Chiron to trap its bishop. Chiron gave a second pawn to open the king side, and launched a strong attack. Jonny exchanged pieces to defend, this led to a QRR vs QRN position with Jonny two pawns up. However, the white rooks were strong with many open files and the black king was exposed, the game was soon adjudicated a win for Chiron.

Ethereal - ChessBrain: Ethereal was a pawn up early in the game. In a series of exchanges ChessBrain gave a rook for a knight and only QRR vs QRN remained, ChessBrain a pawn up. Ethereal traded down to a R vs N ending and an easy win.

ChessBrain - Chiron: The white king was too exposed, Chiron used a queen and bishop combination on the long diagonal to force the king back to the center. Then Chiron doubled rooks in an open file on the queen side and caught ChessBrain's queen in a pin. The game was adjudicated with Chiron a rook up.

ChessBrain - Laser: ChessBrain had an eval advantage of over 1 despite having a knight pair against Laser's bishop pair. The game reached a RN vs RB position, ChessBrain controlled the 7th rank and it slowly captured black pawns. When it was 3 pawns up ChessBrain exchanged rooks and the game was adjudicated.

Laser - Ethereal: Laser tried to weaken the black king side with a knight for pawn sacrifice, Ethereal turned this into a R vs NN imbalance with a growing eval advantage. Ethereal refused to exchange pieces, its eval jumping over 3 as it created an advanced passer in the center. Laser only had major pieces and could not afford to exchange with a black knight defender. The game was adjudicated when the passer reached the 2nd rank.

Booot - Chiron: Chiron opened the h file, and then very slowly it managed to move a rook and queen to the open file to threaten the white king. Chiron's attack pushed Booot's king to the center and after exchanging most pieces only R vs BN remained. Chiron played the endgame slowly, exchanging pawns until only one black pawn was left in a winning tablebase position. First Booot loss that was not a crash. 

Featured game: Laser - Chiron
Division 1, round 7
Link to game on TCEC

The opening looked drawish, evals were close to 0. Laser moved its knights to the king side and Chiron noticed the DS bishop was blocked and attacked it with a pawn. Laser sacrificed the bishop and opened the king side taking pawns with its knight.



Chiron thought its king was still safe. Chiron created a passer on the queen side, and Laser ignored it and continued to move pieces to the king side. When Chiron realized it was in trouble evals jumped over 2, despite having a passer on the 2nd rank.



Chiron lost its passer and Laser closed in on the black king, forcing Chiron to give its queen. Chiron countered with an attack on the white king, now Laser had to give its queen to escape. The game reached a RBN vs RRB position, Laser two pawns up and evals close to 4.



The black pawns were all on light squares, easy targets for the white bishop. Laser soon captured all the black pawns and was 4 pawns up, enough for a win.

Season 13 division 2 statistics

Draw rate, wins



Final draw rate was 64.3%.


Game termination

The three most common game termination causes were:
29.5% - TCEC draw rule
28.6% - TCEC win rule
22.3% - SyzygyTB

There were 3 crashes in the division.

Moves per game



Median= 61.3
Average= 66.0

There were 12 games longer than 100 moves, the longest was 173 moves (ChessBrain - Ethereal, round 27, draw). 

Time per game (hours)



Median= 1:12
Average= 1:11

Openings

There were 2-move book openings in this stage chosen by Cato. Each opening was repeated 4 times in a round, and then again in the reverse games round. In total 14 2-move openings were used. The first letter of the ECO codes was distributed as follows:



If we use the opening 'family name' (using format FAMILY_NAME: VARIANT....) the top 3 are:
Sicillian - 20 times
Queen's pawn game - 19 times
Philidor - 9 times

The engines had a lot of freedom to choose the opening variant. However, 51.8% of the game pairs repeated the same ECO code twice, and 42.9% repeated the same opening variant. In 16.1% of the game pairs the ECO first letter was not repeated twice.

Reverse pairs, wins



Reverse pairs, same moves 



Pairs of reverse games diverged very quickly, 80.3% of the pairs diverged at most after 1 move. The longest repeated move sequence in a game pair was only 7 plys long.  

Season 13 division 2 final results

Division 2 final crosstable



Ethereal and ChessBrain promote to division 1, Arasan and Vajolet are relegated to division 3.

The final draw rate was 64.3%.

ChessBrain dominated the division from the start, consistently beating the weaker engines and almost never losing a game. This was quite a surprise, in season 12 ChessBrain was not so strong in division 2. The fact that ChessBrain is written in Visual Basic also makes it unique. Ethereal had a slow first half with only two wins. Then in RR3 it scored an outstanding 6.5/7 points and reached first place. Ethereal completed the division with no loss, similar to its result in division 3.

The race against relegation was much closer. After RR3 the bottom of the table was Texel -1, Gull -2, Arasan -3, Vajolet -4, Nirvana -6. Vajolet also had 2 early crashes, restricting the number of threads stopped it from being disqualified but this made it an automatic loser in tiebreaks. In round 22 Vajolet beat Nirvana in black, with the help of tablebase support that Nirvana didn't have. In the following rounds Vajolet lost twice to Ethereal and Xiphos while Gull blundered late in the game against ChessBrain in what should have been a draw. With 3 rounds left the scores were Texel -1, Gull -3, Arasan -3, Vajolet -5, Nirvana -7. In round 26 Nirvana converted an early pawn advantage against Arasan and opened up the race. Then in round 27 Nirvana beat Texel in black and Arasan lost again with a blunder against Xiphos. The scores before the last round were Texel -2, Gull -3, Arasan -5, Vajolet -5, Nirvana -5. Texel was safe, and after Nirvana and Arasan drew their games Gull was also safe, despite its loss to Ethereal. Vajolet needed a win in the last game against Texel, but after a long struggle it lost. The second relegation was decided by a tiebreaker, Arasan had one less win than Nirvana.

Division 1 will start soon with the engines Jonny, Chiron, Fizbo, Booot, Laser, Fritz, Ethereal and ChessBrainVB. Chiron crashed out of the premier division in season 12, if this problem has been fixed it will be very difficult to beat. Ethereal is still aiming higher, it will be interesting to see if it can promote for a third time this season.