Season 20 qualification league

Season 20 started with a short qualification league with 7 engines participating, and 4 engines advancing. A new league 4 was introduced this season, most engines that played in the season 19 qualification league will play there.

The engines in the qualification league are:

New engines: Koivisto, Halogen, Seer, Stash, MrBob
Played in season 19 qualification league: A0lite
Played in season 17 qualification league: Cheese

Final standings

Seer, Halogen, MrBob and A0lite qualify for league 4. 

Seer, Halogen and  MrBob were much better than the other engines, their final order at the top of the table reflected the games they played against each other. At the other end of the table Cheese and Stash lost most of their games.

Koivisto supplied most of the drama in this stage. It crashed 7 times, including all its games against the top 3 engines, but it won the remaining 5 games. There was a change of rules in this season and engines were not disqualified after 3 crashes. Koivisto was close to qualifying despite its crashes, but it crashed in the last round and A0lite won its last game, finishing in 4th place 0.5 points ahead of Koivisto.

Scores without Koivisto games: Seer +6, Halogen +4, MrBob +2, A0lite +1, Cheese -6, Stash -9.

Two more changes in season 20:
- The win rule has been canceled, decisive games continue until mate or a tablebase position.
- r-mobility has been added as a second tiebreak criterion, replacing crashes.

The 4 qualifiers will join Monolith, ChessFighter, FabChess, Weiss, Tucano and Bagatur (all from season 19 qualification league) in league 4.

Interesting games

Game 2, Halogen - MrBob: MrBob blundered in a rook ending, Halogen sacrificed its rook and won with 3 connected passers.

Game 5, Cheese - Halogen: Cheese used zugzwang to capture a crucial passer in a knight vs pawns ending. Halogen couldn't protect all its remaining pawns with its king alone.

Game 6, A0lite - Koivisto: A0lite's attack on the king side was blocked by a well timed pawn move. Koivisto opened a file on the queen side and forced mate.

Game 18, Halogen - Seer: Seer exposed the white king with a bishop sacrifice, the attack ended in a RN vs Q ending. Halogen had to use all its pieces to block a passer on the 2nd rank, the black king was free to capture pawns and force a win.

Game 21, Cheese - A0lite: A0lite was probably in a winning position in a queen ending with a passer on the 2nd rank. However it failed to convert, Cheese gave checks with its queen and A0lite didn't find a way to avoid this. Pawn moves kept the game alive, A0lite lowered its eval for the draw rule only on move 224.

Scores after 21 games (scores including Koivisto games in parentheses): Seer +3 (+4), Halogen MrBob +1 (+2), (Koivisto -2), A0lite +0 (-1), Cheese -1 (+0), Stash -4 (-5).

Game 25, Seer - MrBob: Seer went a pawn up early, that was enough for a win in a B vs N ending.

Game 27, Koivisto - A0lite: Koivisto was up a pawn in a QRR vs QRR position. A0lite allowed the pieces to be exchanged, leading to a king and pawns ending that was a white win.

Game 28, A0lite - Halogen: A0lite sacrificed a knight to expose the black king but then avoided a repetition draw which allowed Halogen to reduce to a winning endgame. 

Game 37, MrBob - A0lite: A0lite seemed to have an advantage, but it failed to see a repetition draw that followed a queen sacrifice by MrBob.

Game 41, Koivisto - MrBob: Koivisto was in a promising position, heading towards a rook ending with a pawn advantage and an eval close to 3. Then it crashed on move 53.