The number of possible chess positions is far smaller than the number of possible chess games. So a lot of games have positions in common. I wonder which games intersect in which positions. Aside from the trivial case, whereby every game has a common position with every other game – the opening position.
Then, I want a position that occurs in two games, once for the white player and once for the black player – the position remains the same, but the pieces swap colors. The second requirement is that the next move in both games be a move to the same field and with the same type of piece.
A search engine should be able to understand this, and output a position which conforms to the above requirements, along with the two associated games:
[Event “Lodz”|Site “Lodz”|Date “1938.??.??”|Round “1”|White “Kolski, Jakub”|Black “Appel, Israel”|Result “1/2-1/2″|ECO “E16”]1. d4 Nf6 2. c4 e6 3. Nf3 b6 4. g3 Bb7 5. Bg2 Bb4+ 6. Bd2 Be7 7. Nc3 Ne4 8. Nxe4 Bxe4 9. O-O O-O 10. Bc3 d5
And a half a century later:
[Event “Budapest”|Site “Budapest”|Date “1994.??.??”|Round “1”|White “Schnelzer, Reinhard”|Black “Leroy, Adrien”|Result “1-0″|ECO “E18”]1. Nf3 e6 2. c4 Nf6 3. g3 b6 4. Bg2 Bb7 5. O-O Be7 6. d4 O-O 7. Nc3 Ne4 8. Bd2 Nxc3 9. Bxc3 Be4 10. d5
This kind of competition for the same field (d5 in this case) is not common, because it breaks the white/black symmetry implicit to a position conformant to the described constraints. Admittedly, the “same field” and “same piece” clauses were a bit contrived.
Speaking of contrived constraints: Give me two games, where a part of the first game, is the same as a part of the other in reverse! Or give me all the games, where a check-mate in one (or in two or in three …) was missed by the looser. Or by either player. Was ever a game played (by grand-masters) where someone forced the other one to check-mate him? (Yes, there was.) Identify all the Zugzwangs! And so on – the possibilities are practically endless.
This is not so much about chess (or even search engines) as it is about the complexity, which is visible only with via computer algorithms digesting data (big or small). It is important to understand that not only do we not have all the answers, we do not even have all the questions. Computer algorithm, please tell me what to ask you!