The puzzles are found by a program of our own: it goes through the games of the sources move by move and lets Stockfish 19 check the positions. It keeps positions in which one move is clearly better than all others – with a mate the fastest way counts, a slower mate beside it does not rule the puzzle out. The solution is the line Stockfish computed; if at a later move several moves mate just as fast, each of them is right. Without mate a move at a later step at most 0.3 pawns weaker is right too – then the board says which move was better. If a move just as strong, with the best reply, leads to a new position that meets the same rule, it becomes a puzzle too – marked as a side line, since it did not occur in the game. The motif is recognised by rules of thumb, the level estimated from what makes the solution hard: quiet moves, sacrifices, moves Stockfish only finds at a greater depth. Positions that occur in several games are collected on the page Déjà vu.
Players, place, date and opening come unchanged from the game data; every puzzle leads to its game on chesstoteles.
