Consider those two things interesting to chess fans:
A) The longest checkmates.
B) Immortal games, like e.g. Kasparov's Immortal.
A logical combination of those interests is "the longest (non-trivial) middlegame checkmates". How long can a (non-trivial) middlegame attack be? Seems like an important topic about exploring the limits of chess' complexity. But that topic is unexplored.
The current length records are all about the endgame (tablebase records) or are in some sense "trivial", using very specific tricks to achieve length (e.g. repeated zugzwang).
.....
DEFINING MIDDLEGAME AND TRIVIALITY
How do we define a "middlegame"? How do we define "triviality"?
Instead of defining it directly, I think a better approach is to consider parameters which make the length of a checkmate objectively harder to achieve:
* (Positive.) The amount of pieces on the board.
* (Positive.) The amount of pieces which make a move in the checkmating variation.
* (Positive.) The amount of heavy pieces. Rooks and queens.
* (Positive.) The amount of non-check moves.
* (Positive.) The size of material disadvantage of the checkmating side.
* (Negative.) The amount of obvious repetitions.
* (Negative.) The degree of isolation of pieces. For example, if a piece is 100% isolated from the game forever, it's bad.
As the positive parameters go up and the negative parameters go down, the length of a checkmate becomes objectively harder to achieve. Also, note that many of those parameters have to be evaluated throughout the entire checkmating variation, not only in the initial position. If a complicated middlegame simplifies into a technically won endgame, the technically won endgame doesn't count as adding length.
So, instead of a single definition of a "non-trivial middlegame checkmate", think about a PARAMETER SPACE we can explore. I know, it's inconvenient that there isn't a single simple definition for the task at hand. But that doesn't make the topic less important. If we care about chess, we should care about the maximal length of middlegame attacks. We should care about DIFFERENT types of length records, not just about 1 or 2 types.
.....
HOW TO RESEARCH THAT?
I think there's two main avenues of research.
The first is analyzing computer games. They contain the longest and most sound middlegame attacks.
The second is creating chess positions.
I'll share some of my puzzles. Then some of the other people's compositions and some computer games.
.....
MY PUZZLES
Disclaimer: all positions here were verified with 40MB browser Stockfish, it potentially could've missed something.
Above is a checkmate in 32 moves. At every half-move White is at least 31 points of material down. White never gains material advantage. Queens never get traded off. No piece is forever isolated from the game. Checkmating the Black King requires finding A LOT of completely original moves, no repetition. The entirety of the checkmate takes place in the middlegame.
Above is a checkmate in 34 moves. At every half-move Black is at least 16 points of material down.
Above is a checkmate in 34 moves. At every half-move White is at least 126 points of material down.
Above is a checkmate in 46 moves. At every half-move White is at least 26 points of material down. One flaw of the position is that it contains a bunch of cheap repetitions at the beginning.
A version without cheap repetitions in 43 moves long. 43 moves of pure neverending middlegame, neverending king hunt.
Above is a checkmate in 52 moves. At every half-move the material balance is at least equal.
Sadly, the checkmate has three problems. The biggest problem: Black can make a draw on the 24th move. Smaller problem: White can checkmate much faster in one variation (10th move). But that could be written off as White deciding to go for a longer checkmate on purpose. A microscopic problem: Black can prolong the game by giving White material advantage (on 25th move). But that fact doesn't delegitimize the 52 move checkmate variation at all, it still has to exist.
Above is a seemingly 100% forced checkmate in 52 moves. One flaw is that it has too much nonsensical repetitions at the beginning. It's a modified version of a position from u/thebroward (Reddit).
.....
CONCLUSIONS
Even illegal positions don't make creating a long non-trivial middlegame checkmate easy.
The longest non-trivial checkmate may be only 50+ moves long. We never gonna know where a hard ceiling will hit, but it's definitely got to be less than 100 moves.
Finding "the longest non-trivial middlegame draw" is more complicated than finding the longest non-trivial middlegame checkmate.
Many positions with long (30+ moves) non-trivial checkmates were built from positions from real games. It gives many positions a kind of unique and recognizable look. Underneath all the insanity those positions look "vaguelly typical".
.....
OTHER PEOPLE'S COMPOSITIONS
This composition by Steffen Slumstrup Nielsen has the following properties. White is at least down a piece for the first 26 moves. At least two heavy pieces are on the board for the first 21 moves. It IS a long non-trivial attack, despite being closer to an endgame.
This composition by Philip Bondarenko is unique, because it shows the longest checkmate given the biggest material disadvantage (13 points of material) with the maximal freedom of movement (all Black's rooks are centralized and not blocked by anything except themselves).
It's "trivial" in terms of all moves being checks and there being an obvious repeating pattern, but it maximizes other non-trivial factors (freedom of movement and material disadvantage, with the focus on the latter).
This is a modified version of a position by Rewan Demontay. It has TONS of repetition, so this checkmate is "trivial". But it still explores an important theoretical limit. Something like "the longest checkmate given the biggest material disadvantage and pieces which are not 100% isolated from the game". White is down at least 60 points of material for 51 moves.
.....
COMPUTER GAMES
In the game **Stoofvlees vs. Igel**, there happened a noteworthy 21 move sequence. Throughout which White were down at least 5 points of material (not every half-move, but every move), at least 2 queens and 5 heavy pieces overall remained on the board.
In the game **Torch vs. Leela Chess 0**, there happened a noteworthy 20 move sequence.
So, even with computer games finding a 25+ move attack down material is not trivial. But my knowledge of computer chess is extremely limited.
.....
WHAT YOU CAN DO WITHOUT TOO MUCH EFFORT
You can post here a legal position with a forced 10+ move checkmate (the longer, the better). I could try expanding the checkmate. That's how I created most of my puzzles, the original positions came from my bullet games. And one of the positions I was lucky to find on Reddit.
A) The longest checkmates.
B) Immortal games, like e.g. Kasparov's Immortal.
A logical combination of those interests is "the longest (non-trivial) middlegame checkmates". How long can a (non-trivial) middlegame attack be? Seems like an important topic about exploring the limits of chess' complexity. But that topic is unexplored.
The current length records are all about the endgame (tablebase records) or are in some sense "trivial", using very specific tricks to achieve length (e.g. repeated zugzwang).
.....
DEFINING MIDDLEGAME AND TRIVIALITY
How do we define a "middlegame"? How do we define "triviality"?
Instead of defining it directly, I think a better approach is to consider parameters which make the length of a checkmate objectively harder to achieve:
* (Positive.) The amount of pieces on the board.
* (Positive.) The amount of pieces which make a move in the checkmating variation.
* (Positive.) The amount of heavy pieces. Rooks and queens.
* (Positive.) The amount of non-check moves.
* (Positive.) The size of material disadvantage of the checkmating side.
* (Negative.) The amount of obvious repetitions.
* (Negative.) The degree of isolation of pieces. For example, if a piece is 100% isolated from the game forever, it's bad.
As the positive parameters go up and the negative parameters go down, the length of a checkmate becomes objectively harder to achieve. Also, note that many of those parameters have to be evaluated throughout the entire checkmating variation, not only in the initial position. If a complicated middlegame simplifies into a technically won endgame, the technically won endgame doesn't count as adding length.
So, instead of a single definition of a "non-trivial middlegame checkmate", think about a PARAMETER SPACE we can explore. I know, it's inconvenient that there isn't a single simple definition for the task at hand. But that doesn't make the topic less important. If we care about chess, we should care about the maximal length of middlegame attacks. We should care about DIFFERENT types of length records, not just about 1 or 2 types.
.....
HOW TO RESEARCH THAT?
I think there's two main avenues of research.
The first is analyzing computer games. They contain the longest and most sound middlegame attacks.
The second is creating chess positions.
I'll share some of my puzzles. Then some of the other people's compositions and some computer games.
.....
MY PUZZLES
Disclaimer: all positions here were verified with 40MB browser Stockfish, it potentially could've missed something.
Above is a checkmate in 32 moves. At every half-move White is at least 31 points of material down. White never gains material advantage. Queens never get traded off. No piece is forever isolated from the game. Checkmating the Black King requires finding A LOT of completely original moves, no repetition. The entirety of the checkmate takes place in the middlegame.
Above is a checkmate in 34 moves. At every half-move Black is at least 16 points of material down.
Above is a checkmate in 34 moves. At every half-move White is at least 126 points of material down.
Above is a checkmate in 46 moves. At every half-move White is at least 26 points of material down. One flaw of the position is that it contains a bunch of cheap repetitions at the beginning.
A version without cheap repetitions in 43 moves long. 43 moves of pure neverending middlegame, neverending king hunt.
Above is a checkmate in 52 moves. At every half-move the material balance is at least equal.
Sadly, the checkmate has three problems. The biggest problem: Black can make a draw on the 24th move. Smaller problem: White can checkmate much faster in one variation (10th move). But that could be written off as White deciding to go for a longer checkmate on purpose. A microscopic problem: Black can prolong the game by giving White material advantage (on 25th move). But that fact doesn't delegitimize the 52 move checkmate variation at all, it still has to exist.
Above is a seemingly 100% forced checkmate in 52 moves. One flaw is that it has too much nonsensical repetitions at the beginning. It's a modified version of a position from u/thebroward (Reddit).
.....
CONCLUSIONS
Even illegal positions don't make creating a long non-trivial middlegame checkmate easy.
The longest non-trivial checkmate may be only 50+ moves long. We never gonna know where a hard ceiling will hit, but it's definitely got to be less than 100 moves.
Finding "the longest non-trivial middlegame draw" is more complicated than finding the longest non-trivial middlegame checkmate.
Many positions with long (30+ moves) non-trivial checkmates were built from positions from real games. It gives many positions a kind of unique and recognizable look. Underneath all the insanity those positions look "vaguelly typical".
.....
OTHER PEOPLE'S COMPOSITIONS
This composition by Steffen Slumstrup Nielsen has the following properties. White is at least down a piece for the first 26 moves. At least two heavy pieces are on the board for the first 21 moves. It IS a long non-trivial attack, despite being closer to an endgame.
This composition by Philip Bondarenko is unique, because it shows the longest checkmate given the biggest material disadvantage (13 points of material) with the maximal freedom of movement (all Black's rooks are centralized and not blocked by anything except themselves).
It's "trivial" in terms of all moves being checks and there being an obvious repeating pattern, but it maximizes other non-trivial factors (freedom of movement and material disadvantage, with the focus on the latter).
This is a modified version of a position by Rewan Demontay. It has TONS of repetition, so this checkmate is "trivial". But it still explores an important theoretical limit. Something like "the longest checkmate given the biggest material disadvantage and pieces which are not 100% isolated from the game". White is down at least 60 points of material for 51 moves.
.....
COMPUTER GAMES
In the game **Stoofvlees vs. Igel**, there happened a noteworthy 21 move sequence. Throughout which White were down at least 5 points of material (not every half-move, but every move), at least 2 queens and 5 heavy pieces overall remained on the board.
In the game **Torch vs. Leela Chess 0**, there happened a noteworthy 20 move sequence.
So, even with computer games finding a 25+ move attack down material is not trivial. But my knowledge of computer chess is extremely limited.
.....
WHAT YOU CAN DO WITHOUT TOO MUCH EFFORT
You can post here a legal position with a forced 10+ move checkmate (the longer, the better). I could try expanding the checkmate. That's how I created most of my puzzles, the original positions came from my bullet games. And one of the positions I was lucky to find on Reddit.
