Rule 16.2

En-passant convention. An en-passant capture on the first move is permitted only if it can be proved that the last move was the double step of the pawn which is to be captured

The AP Agreement.

I don't have an official text. But the principle is that if by castling we can, for example, prove the possibility of e.p., then it is allowed to do e.p. first, and to do the proof (castling) later.

The first AP tasks appeared about a hundred years ago and were somehow solved. The first Codex (Piran) appeared in 1958. And the note 14 can be attributed to the AP there.

Aus der Vermutung, dass K und T noch nicht gezogen haben, eine Rochade also noch zulässig sein soll, dürfen keine retroanalytische Schlüsse gezogen werden; es ist vielmehr notwendig, dass die Rochade auch ausgeführt wird.

Pay attention to an important point. The position of the king and the rook in the castling position is not the basis for retroanalytical conclusions. Confirmation of the right to castling can only be the execution of castling.


What is the essence of the problem? We need to define a step-by-step implementation of the AP convention. That is, a strict procedure.

  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Chess Meta, or in Chess Chat. Comments continuing discussion may be removed.
    – Brian Towers
    Commented Jul 6 at 9:59
  • Without an official wording of the AP Agreement, we really have nothing to even start from in the dispute. Commented Jul 7 at 16:11
  • Unfortunately, there is no official wording of the AP Agreement in nature. For some reason, they forgot to write... Commented Jul 7 at 16:13
  • The question can be closed. Commented Jul 7 at 16:13
  • Maybe just delete it yourself. We have plenty of other questions :-)
    – Laska
    Commented Jul 8 at 9:29

1 Answer 1


Taking into account the newly discovered circumstances (the absence of an official wording of the AP agreement) and taking into account the fact that the AP principle itself does not cause disagreement (in Petrovich's type, this is the fulfillment of an optimistic move as proof of the legality of the fulfillment of a pessimistic move made earlier), the user decides on his own the issue of interaction with rule 16.2.

And two main approaches can be formulated.

Approach 1. Ordinary.

  1. We are making a pessimistic move.
  2. We are making an optimistic move, proving the legality of paragraph 1.

Interaction with rule 16.2 occurs after the fact at the time of castling.

Approach 2. Creative (see explanation 1)

  1. White makes a statement that they have the right to castling.
  2. Based on this statement, they are making a pessimistic move.
  3. By performing an optimistic move, they prove the truth of the statement made.

The interaction with rule 16.2 takes place at the very beginning (BEFORE the pessimistic move is made).


Explanation 1.

The "creative" approach implies that we consider the process of solving a problem not as a game with ourselves, but as a real confrontation. Relatively speaking, we imagine that a real person is playing for black, who will use any of the most intricate points of the rules to protect himself. And you can even imagine that there is a third real person. A judge who will resolve disputes between us.


When solving the overwhelming number of tasks, the applied approach does not matter. Both will lead to the same result.

There are two cases where there is a difference (there may be more).

1. Maximummer (type Petrovic).

To decide on the second approach, an additional line of the decision will be required to substantiate the statement (the ability to prove the statement made). An important point! You cannot require the mandatory presence of an additional line in the solution of the problem, because it can be solved in the first way, where it is not necessary. And also, a solution with an additional line cannot be considered incorrect. In the applied logic, only it is correct. Given that the procedure is not described, we cannot declare that only one solution is correct. Both are true - only the logic is different.

AP (type of Keym, black)

Here, the second (creative) approach is certainly more logical. At least, it is clear why we are considering the option at all (A move in black's position). With the first approach, the very grounds to consider the option that black may have a move in the position look rather contrived. As we say, "pull by the ears" (притянутыми за уши, far- fetched).

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