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I was thinking about some rules and I got a really nice question. Can we castle with a promoted pawn-rook?

If the rules are not threatened. The King had not moved before, he is not passing a square under attack. And the new rook has not moved too. It is a bigger question if it's useful and if somebody will ever use that, but for me, it seems to be a legal move.

If yes, how would this castling look like?

Ke3 Re2?

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    The promoted Rook is on the eight rank, the King, not to have moved, must be on the first rank: how would castling be even possible? – gented Jul 19 '17 at 20:42
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    Please take a look at the pictire of @RemcoGerlich. It is showing this possition. It even was possible before. But now it is restricted by rules. So my question I actually not so bad. I do not understand why somebody is downwoting it. – Predicate Jul 20 '17 at 16:16
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No, according to FIDE's Laws of Chess, castling has to be done along the first rank.

§3.8.2:

3.8.2 by ‘castling’. This is a move of the king and either rook of the same colour along the player’s first rank, counting as a single move of the king and executed as follows: the king is transferred from its original square two squares towards the rook on its original square, then that rook is transferred to the square the king has just crossed.

3.8.2.1 The right to castle has been lost:

3.8.2.1.1 if the king has already moved, or

3.8.2.1.2 with a rook that has already moved.

3.8.2.2 Castling is prevented temporarily:

3.8.2.2.1 if the square on which the king stands, or the square which it must cross, or the square which it is to occupy, is attacked by one or more of the opponent's pieces, or

3.8.2.2.2 if there is any piece between the king and the rook with which castling is to be effected.

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    The rules have evolved over time to exclude more and more of these obscure possibilities. The loopholes are often pointed out / discovered by problemists who produce impossible looking problems which rely on some strange loophole in the rules. Another clever one is that when you promote a pawn it must be to one of your pieces not your opponent's. Old rules didn't have this restriction until someone produced a mate in 1 problem relying on a pawn promotion which uncovered a check with the promoted piece being an opposition knight taking away a flight square from the king. – Brian Towers Jul 19 '17 at 21:13
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This question really needs a diagram with this position:

[FEN "8/8/4P3/3p4/2p3p1/1pP1kPPp/1P5P/R3K2R w KQkq - 0 1"]

White to mate in 3.

Tim Krabbé and Max Pam found the loophole in the rules that you are asking about -- when they composed this problem in 1972, the promoted rook did indeed enable castling, as the rules only talked about a rook that hadn't moved yet! The rule was changed because of this problem.

The solution is beautiful as there are three different castlings involved:

  1. 1.e7 Kd3 2.e8=R gxf3 3.0-0-0#.
  2. 1.e7 Kxf3 2.e8=R d4 3.0-0#.
  3. 1.e7 Kxf3 2.e8=R Kg2 3.0-0-0-0#!.
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    I guess white has to promote to a rook in the first variation also, so that 2... Kc2 can be answered by extra long castling. – Dag Oskar Madsen Jul 20 '17 at 13:16
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    @DagOskarMadsen: that's what I get for just typing variations from a Google hit... it's more symmetrical too – RemcoGerlich Jul 20 '17 at 13:19
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    Although 3.Qe2# also works in that case. – RemcoGerlich Jul 20 '17 at 13:21

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