Nested Chess

This variant came about through the duality between the cubic-cell geometry and that of my recent variant OctHex 146, in which the orthogonals or each correspond to the diagonals of the other. In 2d the duality is much simpler: the square-cell geometry is its own dual, perhaps unsurprising given that the numbers of orthogonal and diagonal directions are both 4.

My first thought was to start with the FIDE array and stick extra cells at the cell vertices. This raises the question of which edge vertices to include. I discounted excluding all 32 as this would leave the transformed pieces on edge diagonals. I decided to include all but the corner ones.

I looked at what the FIDE pieces had become. The Pawns had become something a bit new, but a name came to mind for that. The simple pieces remained familiar (though different). It was only with the middle pair that I was unhappy, as they lacked long-standing names. One was the one that I termed Fezbaba in Turn Qi and subsequently in Symgi. The other was the rider of that piece, and I thought that having both might be confusing.

I therefore decided to make the hidden array the Mongolian Chess one, which in place of the Queen has a Rook+Ferz piece - Chatelaine in my terminology. This transforms into Bishop+Dabbaba, for which I also have a distinctive name. Following the Mongolian lack of special moves also simplified the variant greatly, although I felt a duty to do something with at least that variant's "no Checkmate by Knight" element.

The final stage was to add original pieces back on the edge diagonal behind the transformed pieces. This meant Rooks at each end and Knights next in, with the King in the middle. Bishops needed not be added as these were what the original Rooks had become, so I added pieces reversing the orthogonal and diagonal significance of the transformed central pair.

As an afterthought I added a second array, based on a corner. Forward-only pieces are affected by which is used, as the first has two forward orthogonals and one forward diagonal, and the second vice versa. I thought it more interesting to try both out.

I have since added the following offshoots of this variant:Nested Shogi, Nested Xiang Qi, and Doubly Nested Chess.

Setup

Variant B

Pieces

Royal and semi-royal:

	The KING is the usual royal piece that moves one square in any radial direction and must be kept out of check.
	The FEZBABA moves two squares orthogonally or one diagonally. The name is derived from its components the Ferz and Dabbaba. A player without a Fezbaba cannot move their bound pieces, but unbound pieces are unaffected.
	The WAFFLE moves one square orthogonally or two diagonally. The name is derived from its components the Wazir and Alfil or leaping Elephant. A player without a Waffle cannot move their unbound pieces (except the King), but bound pieces are unaffected.

	The BISHOP moves any distance diagonally through empty intermediate squares. It results from transforming the original Rook.
	The CAMEL makes any 3:1 leap, and cannot be blocked. It results from transforming the original Knight. A Camel capturing the enemy Fezbaba makes their own Fezbaba disappear as well, simulating the Mongolian ban on Checkmate by a Knight. A Camel can Check and Checkmate the actual King normally.
	The DABBARIDER moves an even number of squares orthogonally, and can leap over intervening pieces on odd but not even squares. It results from transforming the original Bishop.
	The INQUISITOR is a Bishop that can also leap two squares (but not just one) orthogonally. Note that it can be blocked diagonally but not orthogonally. The name is the title of a historic religious figure especially associated with the same land as the Infanta (see below) and gives Inquisition Ashtaranga its name. The piece results from transforming the original Chatelaine.
	The ESQUIRE moves one square diagonally forward (one possible direction in variant A, two in variant B), except when capturing, when it moves two squares orthogonally forward (two possible directions in variant A, one in variant B). When capturing it can leap over an intervening piece. The name refers to a man below the rank of Knight; I use the longer form because it has been used less often (if at all) for other pieces than the shorter Squire and avoids sharing the first five letters of Squirrel. The piece results from transforming the original Pawn. See also my piece article Man and Beast 16: Diverging Further.

	The ROOK moves any distance orthogonally through empty intermediate squares.
	The KNIGHT makes any 2:1 leap, and cannot be blocked. A Knight capturing the enemy Waffle makes both Waffles disappear, extrapolating from the Camel x Fezbaba rule.
	The INFANTA is a Rook that can also leap two squares (but not just one) diagonally. Note that it can be blocked orthogonally but not diagonally. The name is after the association, whether real or apocryphal is much debated, between the Spanish princess the "Infanta de Castile" and the pub name "Elephant and Castle".
	The PAWN moves one square orthogonally forward (two possible directions in variant A, one in variant B), except when capturing, when it moves one square diagonally forward (one possible direction in variant A, two in variant B).

Rules

There is no initial double-step move, En Passant, Castling, or Cathedralling, as Mongolian Chess has none of these.

A Pawn reaching a symmetric enemy piece's starting cell or an edge diagonal must be promoted. It can be promoted to any unbound piece except a King or Waffle. It can also be promoted to a Fezbaba if it is not on an edge diagonal and the player no longer has a Fezbaba. The latter promotion reactivates the player's bound pieces.

An Esquire reaching a symmetric enemy piece's starting cell or an edge diagonal must be promoted. It can be promoted to any bound piece except a Fezbaba. It can also be promoted to a Waffle if the player no longer has a Waffle. The latter promotion reactivates the player's unbound pieces.

Check, Checkmate, and Stalemate are as in FIDE Chess. The bar on a player exposing their King to Check includes through their Fezbaba or Waffle disappearing by double capture. They can of course expose the enemy King to Check by this means.

Notes

Last revised by Fergus Duniho.