How Koga decides

Idea An in-between move that delays a recapture
  • An intermezzo is a forcing move slipped in BEFORE the recapture the opponent is waiting for. Instead of taking back immediately, we play something more urgent first.
  • The point: the recapture is still available, so we play the urgent move now, force a reply, and only then take back — having gained something extra in between.
Pattern What Koga looks for
  • A capture on some OTHER square was available right now — the move we could have made instead of the in-between move.
  • We play a different move first (the intermezzo).
  • Later in the forcing line we come back and make that delayed capture, with the very same piece-and-destination that was available before.
  • The line must be at least three moves long (in-between move, the forced reply, then the payoff) so the pattern can be confirmed.
Filters When we do NOT call it an intermezzo
  • The opponent's previous move must have been a capture — there must be a genuine ongoing exchange to delay. If they only pushed a pawn or developed a piece onto a square we attack, taking it later is just winning a piece, not an intermezzo.
  • The payoff must land back on the square the opponent just captured on. If we eventually win material somewhere else entirely, the in-between move did not delay this recapture.
  • The recapture must not have been possible before the opponent's move — it is the opponent's capture that created the thing we take back. If we could already have made that capture beforehand, nothing was delayed.

Test positions (the examples that guard against regressions)

Check first, then take

A constructed position. Instead of recapturing at once, White inserts Bxf7+. The king can't take (the e5-knight covers f7), so Black must recapture with ...Qxf7, and only then does the knight come back with Nxc6, collecting the knight that was waiting to be taken. The in-between check is the intermezzo.

✓ detectedCheck intermezzotest_detects_intermezzo_check_before_recapture
r . b . k b . r
p p p p q B p p
. . n . . n . .
. . . . N . . .
. . . . P . . .
. . . . . . . .
P P P P . P P P
R N B Q K . . R
Piece that moves
Attacking piece
Targeted / won piece

A recapture delayed through a forced queen trade

From a Caro-Kann game. Black has just played Nxf4, expecting Bxf4. Instead White plays Qxf7, forking the bishop on f8 and rook on e8. After Nf6, White trades queens with Qxc7+ Kxc7, and only then does Bxf4 finally take the knight on the setup square — four plies after the intermezzo.

✓ detectedLong-delay intermezzotest_intermezzo_with_long_delay_through_forcing_sequence
. . k . r b . .
p p q n . Q . .
. . p . p . . .
. . . p P . B .
. . . P . n . .
. . N . . . . .
P P . . . P P .
. K . R . . . .
Piece that moves
Attacking piece
Targeted / won piece

Golden puzzles — every real Lichess puzzle Koga is tested against for this tactic (10)

Lichess 06Asm

Lichess 06Asm (rating 1407). Solution: Nxe7+ Kf7 Rxf1+ Kxe7 Bxc5+.

✓ detectedrating 1407♟ Lichess 06Asm
. . . . . . k .
. . . . b . p p
p . N . p . . .
. . n . . . . .
r . . . . . . .
. . . . B . P K
. . . . . . . P
. . . R . r . .

Lichess 01X6J

Lichess 01X6J (rating 1475). Solution: Qe4+ Kg1 Bxf5.

✓ detectedrating 1475♟ Lichess 01X6J
r . b . q k n Q
. . . . . . p .
. . . . . . P .
p . . p . N R .
. . . . . P . .
. P . . p . . .
P . P . . . . P
. . . . R . . K

Lichess 0155R

Lichess 0155R (rating 1384). Solution: Rxf1+ Kxf1 Qxf7 Qxf7+ Kxf7.

✓ detectedrating 1384♟ Lichess 0155R
. . . . r . k .
p p . . q R . .
. . . p . . p B
. . n P . . . .
P . P . . . . .
. . P . . . . .
. . . . . Q P P
. . . . r R K .

Lichess 00Htd

Lichess 00Htd (rating 963). Solution: Bxc3+ bxc3 Qxd5.

✓ detectedrating 963♟ Lichess 00Htd
r n b q k . . r
. p . . . p p p
p . . . . b . .
. . P Q . . . .
. . . . . . . .
. . N . . N . .
P P . . P P P P
R . . . K B . R

Lichess 06kDo

Lichess 06kDo (rating 1834). Solution: Rxe5 dxe5 Bxd5.

✓ detectedrating 1834♟ Lichess 06kDo
. . . . r . . .
p . . . r . k .
. p . . . . . p
. . . B R . p .
q . . P b . . .
P . P . Q . P .
. P . . R . . P
. . . . . . K .

Lichess 05gDD

Lichess 05gDD (rating 1604). Solution: Rxa2 Qxa2 Qxb4.

✓ detectedrating 1604♟ Lichess 05gDD
. . . . . . . .
. . . . . . . .
q . . . k . p p
. p . p . p . .
. b . P . P . .
. . Q . P . . P
r B . . . . P .
R . . . . . K .

Lichess 04XmB

Lichess 04XmB (rating 1769). Solution: Rxh7+ Kxh7 dxe5 d4 exd4.

✓ detectedrating 1769♟ Lichess 04XmB
. . . . . . . R
p . . . . . k p
. p . . . . . .
. . . p q p . .
. . . P p . . .
P K . . P . . .
. P . . . P . .
. . . . . . . .

Lichess 01ddN

Lichess 01ddN (rating 1392). Solution: h5+ Kf5 Rxb4.

✓ detectedrating 1392♟ Lichess 01ddN
. . . . . . . .
. R . . . . . R
. . . . . b k .
. . . . . . . .
. r . . . . . P
. . . . r . P K
. . . . . . . .
. . . . . . . .

Lichess 04tM3

Lichess 04tM3 (rating 1654). Solution: Rxc8+ Rxc8 dxe5.

✓ detectedrating 1654♟ Lichess 04tM3
r . r . . . k .
. . . n . p p p
N . . . . . . .
. . R . q . . .
. . . P . . . .
P . . . . . . .
. P . . . P P P
. . . . R . K .

Lichess 00DII

Lichess 00DII (rating 1920). Solution: Re8+ Kf7 Qxd5+ Rxd5 Rxc8.

✓ detectedrating 1920♟ Lichess 00DII
. . r r . . k .
p . . . . . p .
. p . . . . . p
. . p q . p . P
. . . . . . . .
P . . . . Q R .
. . . . . P P .
. . . . R . K .