Paired Piece Tunnelchess

Setup

PAIRED-EVERYTHING TUNNELCHESS

PAIRED-LINEPIECE TUNNELCHESS differs in having a Coheir on every cell of ranks 2 and 7. ORDERS-OF-KNIGHTHOOD TUNNELCHESS replaces these with Garters on the Frame and Tunnel, Thistles in front of the Duchesses and Governors, and Patricians in front of the Bishops and Rooks.

Pieces

	Simple radial linepieces
	The ROOK moves any distance through empty intermediate cells in the 6 orthogonal directions, each of which is the intersection of 2 2d planes and at right angles to the other plane. It is unbound.
	The BISHOP moves any distance through empty intermediate cells in the 12 standard diagonal directions, each of which is a diagonal of a 2d plane and at 45° to the other 2 planes. Each Bishop is bound to half the board.
	The UNICORN moves any distance through empty intermediate cells in the 8 nonstandard diagonal directions, commonly called triagonal, which are all at 35° to all three planes. Each Unicorn is bound to a quarter of the board, which is why there are four of them aside.
	Compound radial linepieces
	The EMPEROR moves one step in any of the 26 radial directions. It is unbound, but must be kept out of Check.
	The EMPRESS is the compound of Rook, Bishop, and Unicorn. It inherits the Rook's lack of binding.
	The QUEEN is the compound of Rook and Bishop. It inherits the Rook's lack of binding.
	The DUCHESS is the compound of Rook and Unicorn. It inherits the Rook's lack of binding.
	The GOVERNOR is the compound of Bishop and Unicorn. The components' independent bindings make the piece unbound.

	In PETC, simple 2:m:n leapers
	The KNIGHT makes any 2:1:0 leap. The zero smallest coordinate indicates that it always moves within one of the three planes, and the single odd coordinate that it is unbound and colourswitching.
	The SEXTON makes any 2:1:1 leap. The nonzero smallest coordinate indicates that it never moves within one of the three planes, the 2 odd coordinates that it has the Bishop's binding, and the largest coordinate being the sum of the others that it can triangulate. The name puns on its Square of Leap Length being 6.
	The NINJA makes any 2:2:1 leap. The nonzero smallest coordinate indicates that it never moves within one of the three planes, and the single odd coordinate that it is unbound and colourswitching. The name puns on its Square of Leap Length being 9.
	In PETC, compound 2:m:n leapers
	The CHURCHWARDEN is the compound of Knight and Sexton. Sextons start on Wall files e and h, beside the Empress and Emperor respectively. The name means a higher ecclesiastical lay rank than Sexton.
	The SAMURAI is the compound of Knight and Ninja. Samurais start on Wall files b and c, directly above the Empress and Emperor respectively. The name means a Japanese warrior of higher rank than a Ninja.
	The OBERON is the compound of Ninja and Sexton. Oberons start on Frame files a and d, diagonally adjacent to the Empress and Emperor respectively. The name, that of a Shakespeare character, is used here to stand for Oblique baron, from the SOLLS of its components being in a ratio of 2:3 like the radial Baron.
	In PETC, Curved radial linepieces
	The CURVED DOUBLE RHINO (Rhino for short in this variant) makes up to 6 steps, alternating between orthogonals and standard diagonals, through empty intermediate cells with a 45° turn at each forming sides of an octagon. It can start with either and end with either. If the a2 Rhino is the first piece moved it can follow the paths a2-a3-b4-c4-d3, a2-a3-e4-i4-m3, a2-b3-b4-a5, a2-b3-c3, a2-e3-e4-a5, or a2-e3-i3. If the b2, e2, or f2 leaper is moved before it this opens up further paths. In 2d this piece appears in John Savard's Leaping Bat Chess.
	The APOSTLE is a Curved Bishop making up to 4 steps along standard diagonals, through empty intermediate cells with a 60° turn at each forming sides of a hexagon. If the m2 Apostle is the first piece moved it can follow the paths m2-i3-f2, m2-i3-j4-o4, m2-n3-j4-e4, and m2-n3-k3. If the j2 Churchwarden is moved first, this opens up the paths m2-j2-f3-e4 and m2-j2-k3-o4. The Apostle shares the Bishop's binding and takes it name from being intermediate between the Bishop itself and the RABBI, the 60° Curved hex-diagonal rider.

In OOKTC, file-dependent movers
The GARTER moves as a Coheir except from the Wall files, taken to represent England (at the ends of a cross of files), whence it moves as a Knight. Named after England's order of Knights of the Garter.
The THISTLE moves as a Coheir except from the Frame files, taken to represent Scotland (at the ends of a saltire of files), whence it moves as a Knight. Named after Scotland's order of Knights of the Thistle.
The PATRICIAN moves as a Coheir except from the Tunnel files, taken to represent pre-WW1 Ireland (where the rulers can keep an eye on them ready for post-WW1!), whence it moves as a Knight. Named after (then all of, now just Northern) Ireland's order of Knights of Saint Patrick.

Rules

In PLTC, Coheirs may be promoted to a stronger capturable array piece on reaching the enemy Coheir rank and must be should they reach the rank beyond. PETC has no promotion. In OOKTC the second rank pieces are promoted on reaching either rank of the enemy camp, optionally if they have another unpromoted move thence and automatically if not. Garter promotion is to Queen on Wall files, Rook on Frame files, and Bishop on Tunnel files. Thistle promotion is to Duchess on Frame files, Rook on Wall files, and Unicorn on Tunnel files. Patrician promotion is to Governor on Tunnel files, Bishop on Wall files, and Unicorn on Frame files.

Check, Checkmate, and Stalemate are as in FIDE Chess.