If piece A has passed over the critical square in order to avoid the hindrance of its influence by some piece B, we say that piece A made an anticritical move.
| Doubling of pieces happens when we put two pieces on the same row (or column or diagonal). Theme Turton doubling : A linear piece A moves beyond a critical square, permitting to a like-coloured and stronger piece B to move onto the critical square. Later piece B moves on the same line to the opposite direction, being supported by piece A. Brunner-Turton doubling : The pieces A and B are equal in value. Loyd-Turton doubling : Piece A is stronger than piece B. Zepler-Turton doubling : Initially the piece A moves. Then piece B steps on the critical square. Then piece A moves again, being supported by piece B. Bicoloured Turton : The pieces A and B have different colours. |
The line opening in problem-19 is not a “Bristol”, because the two pieces which move on the same line, are moving in opposite directions, that means it is a Turton doubling..
 | (Problem 19) Sam Loyd ”Cincinnati Dispatch”, 1858 White plays and mates in 3 moves #3 (4+7) |
| [2s5/6p1/8/5p2/8/7S/3pp1B1/KQ1bk3] | |
Key: 1.Ba8!
The bishop goes up the diagonal h1-a8 (over square b7), in order to make space for the white Qb1, that will move on square b7 and will move down the diagonal and will give mate from square h1).
1...g5 2.Qb7 ~ (the symbol ~ means any move, black plays anything) 3.Qh1#
1...f4 2.Qg6 ~ 3.Qg1#
1...Kf1 2.Qxf5+ Ke1 3.Qf2#
1...Sd6 (does not allow 2.Qxf5 and 2.Qb7) 2.Qb6 ~ 3.Qg1#
In the final picture of mate, Ba8 does not take part, so it is a parasitic piece.
| Theme Cheney-Loyd, is the case when the white piece A makes a critical move and the white piece B goes to the critical square and interferes. Black Cheney-Loyd is the case when the black piece A makes a critical move and the black piece B goes to the critical square and interferes. Bicoloured Cheney-Loyd is like Cheney-Loyd, and the pieces A and B have different colours. |
In the next problem we see the parasitic piece moving to open a line for a piece, which is not giving mate but it is closing flights of the black king, and that means it is a Cheney-Loyd interference.
 | (Problem 20) J. W. Abbot "Baltimore News", 1890 White plays and mates in 3 moves #3 (5+2) |
| [3K4/8/3k4/8/3p4/P2P4/8/2R1R3] | |
Key: 1.Rc8! Kd5 2.Kc7 Kc5 3.Re5#
In this problem the pawn a3 is a revealer : It is a fact that in a problem only the absolutely necessary pieces are included. Seeing the pawn at square a3, we understand that, during the solution the black king will move towards a3.
Parasitic piece here is Rc1. The rook Rc1 must not leave the c-file, in order to force Kd6 to move to square d5. Then the black Kd5 must not return to d6, but must be forced to go to c5 (then, where should the rook of c-file stand ?). And, finally, the mate must occur on the square c5, because no more moves remain.
On the next prized problem-21 the composer Triantafyllos Siaperas presents two themes, Bristol line-clearance and Turton doubling, with a very nice way.
 | (Problem 21) Triantafyllos Siaperas, First Prize, ”S.A.H.”, 1948 White plays and mates in 3 moves #3 (7+7) |
| [SK6/8/PB1p4/1k1bR2Q/1p6/1p6/qp1P4/8] | |
Key: 1.Re1! [2.Qxd5+ [3.Qc4#]]
If 1...Qa4 2.Qe8+ Bc6 3.Qe2#
(That was a Bristol. The white queen moved in the same direction with the rook, on the e-file).
If 1...Qxa6 2.Qe2+ Bc4 3.Qe8#
(That was a Turton. The white queen moved in the opposite direction with the rook, on the e-file).
There is interesting by-play:
1...Qa4 2.Qe8+ Kxa6 3.Qxa4#
1...Qxa6 2.Qe2+ Ka4 3.Qxa6#
1...Qa5 2.Qxd5+ Ka6 / Ka4 3.Qxa5#
[This post in Greek language].
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