[Retros] Again about En Passant Chess
elkies at math.harvard.edu
Sun Mar 25 11:53:10 EDT 2007
>> I don't think this visualization works, because the opponent may
>> have a choice of which billiard ball to activate, and indeed
>> may choose to activate none if the opponent's piece stopped
>> short of its target [...]
>> A nice aspect of your rule that I didn't notice before is that
>> it incorporates the rule forbidding a King from moving through check
>> when castling!
> you are right: no paradoxes.
> The only one could arise if we allow to a piece being captured
> to capture the piece is just going to capture it before that happen!
> If so, who will be captured?
Hm... That looks like a good case for incorporating the condition
implicit in Guus Rol's observation:
| A question to ponder on is whether or not to allow for e.p. captures
| in the same line of action, e.g. wBd2-h6, bBc1xf4 e.p. Though there
| is no iron-clad argument to reject the validity of this type of e.p.
| action, there is a feel that the en passant concept should include the
| property of "cross-firing" which is missing in this type.
Excluding e.p. captures on the same line would automatically take care
of this paradox too.
> But, what we have to do with Knight rules? It just flights
> when it moves, so it could'nt be captured en passant. Right?
That makes sense. Pieces that can be captured e.p. are "line-pieces",
whose path can be obstructed by a man (of either color), and can now
be captured e.p. on any of the potential obstruction squares:
Queen, Rook, Bishop, and also Pawn making a double-move and
King in the process of castling. The Knight is a "leaper",
which cannot be obstructed and should not be subject to e.p. capture.
(A Chinese knight, on the other hand, *can* be obstructed, and thus
should be e.p. capturable on the squares it moves through on the way
to its destination.)
This still leaves the question of whether, after the sequence
1 X:Y, Z:X e.p.; the piece Y should reappear on the board --
and if we answer Yes then do we let Kings be reincarnated in
the same way.
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