The terminology and history of Killer variants has had a long and interesting history. This post is intended to summarize these developments. I briefly summarize some other draughts variants and the relevant historical proposals that were launched in order to limit the drawing percentage in international draughts. Frisian draughts
There is no direct link between Frisian draughts and Killer variants, but some ideas/terminology from draw-limiting proposals derived from Frisian draughts did have an influence on Killer variants.
In Frisian draughts, both men and kings jump both diagonally and orthogonally
. Frisian draughts also has different majority capture precedence and a few other minor differences with respect to international draughts.
In Frisian draughts, 2 kings beat 1 king.H. Hoogland proposal
In 1923, then World Champion H. Hoogland borrowed from Frisian draughts by proposing to let kings capture other kings both diagonally and orthogonally
. The man jumps and the majority capture rules were left in tact. With only kings on the board, the Hoogland proposal reduces to Frisian draughts.
In the Hoogland proposal, 2 kings beat 1 king.A. Renooij / Tj. de Reus proposal
In 1924, A. Renooij proposed to only apply the Hoogland-rule when only kings are left on the board
In 1972, Tj. de Reus rediscovered this proposal. He also introduced the definition phase 3 = only kings on the board
(phase 1 = only men on the board, phase 2 = both men and kings on the board).
In the Renooij/De Reus proposal, 2 kings beat 1 king.Thai draughts
The origin of king-halt restrictions lies in Thai draughts.
A Thai king has to land directly after each captured piece, and start looking for a next jump from that intermediate landing square.
White-to-move has to capture a3xg3 (via d6): white starts to jump a3xd6, and from there, only d6xg3 is possible. White cannot jump a3xe7 in order to continue with e7xg5 and g5xe3.
Note that Thai draughts does not have majority capture precedence, and that you also immediately have to remove a jumped piece, and not when all pieces have been jumped (so the Coup Turc is not possible in Thai draughts).
In Thai draughts, 2 kings beat 1 king.A.K.W. Damme proposal
In 1922, then Dutch champion A.K.W. Damme proposed to use the king-halt rule after the final piece (man or king) only
In the Damme proposal, 2 kings beat 1 king.M. Fayet proposal
In 1924, M. Fayet proposed a very complicated variant. The kings from the first player to get a king (i.e. in phase 1), are regular kings but they are now called major kings
. The kings from the second player to get a king (i.e. in phase 2), are called minor kings
. A minor king will be restricted to both the intermediate and the final king-halt after the first sideways capture
With a white major king, white-to-move has to capture 36x32 (via 18, 34 and 43).
With a white minor king, white-to-move has to capture 36x42. White starts to jump 36x22 or 36x18. From square 22, white can continue to jump 22x44/50 (2 pieces). From square 18, white can continue to jump 18x29, and from there 29x42 (final king-halt applies, so not 29x47), for a total of 3 pieces. White cannot jump 36x18x34x43x32 (4 pieces), because after the first sideways capture, the intermediate king-halt 18x29 applies.
In the Fayet proposal, 3 major kings beat 1 minor king, but 3 minor kings cannot beat 1 major king.Tj. de Reus booklet
In 1989, Tj. de Reus wrote a small brochure where he introduced new terminology and also modified some of the previous proposals. First, he introduced the definition of demotion = a restriction of kings only in phase 3
Second, he used the term Damme-demotion
for the variant where the king-halt of Damme (king-halt after final piece) applies only in phase 3, and the term Fayet-demotion
for the variant where the king-halt of Fayet (intermediate and final king-halt after first sideways capture) applies only in phase 3.
With the Damme-demotion, 2 kings beat 1 king. With the Fayet-demotion, 3 kings beat 1 king.Killer draughts
Somewhere around 2000, C. Freeling introduced Killer draughts by replacing the "only in phase 3" condition of the Damme-demotion with the "only after a final king
Won in Thai draughts, the original Damme-proposal and in Killer draughts. Draw with the Damme-demotion (the king-halt only applies with only kings on the board).
In Killer draughts, 2 kings beat 1 king.Killer light
In 2016, Juri Anikejev introduced Killer-light by replacing the "only in phase 3" and "after the first sideways capture" conditions of the Fayet-demotion with the "only after a final king
" (i.e. no longer intermediate king-halts) and "after the first capture
" (i.e. only in multiple capture sequences) conditions.
White-to-move wins in the original Fayet-proposal (if black has a minor king) and in Killer-light, but not with the Fayet-demotion (the king-halt only applies with only kings on the board).
Note however, that with black-to-move, after 1... 5-46, white could still win against a minor king in the original Fayet-proposal (2. 38-32! 46x39 W+) but not with Killer-light (because the final piece captured is not a king).
In Killer-light, 3 kings beat 1 king.Summary
The king-halt proposals by Damme/Fayet from the 1920s were unconditional on the game phase (i.e. what material is still is on the board) and the last captured piece type.
The king-halts in the demotion variants by De Reus in 1989 were conditional on the game phase (with only kings on the board).
The king-halts in the recent Killer variants by Freeling/Anikejev are conditional on the last captured piece type being a king. Killer-light further removes the restriction in the Fayet variant on intermediate king-halts, and modifies the restriction of at least one sideways capture to only a multiple capture sequence.