Here is a list of checkmates unique to 4PC and their respective definitions. Virtually all checkmate positions from classical chess may still apply in 4PC games. For a list of classical checkmate positions, please click here.

Double Checkmate

A double checkmate is a position in which a players King is in checkmate via means of being in double check without any squares in which to escape to. A player whose King is in double check must move the King on their turn as neither check can be legitamately blocked nor can the checking pieces be captured by the checked players own pieces other than by his King if the checking pieces are unprotected. The following is a list of possible double checkmate classes; though highly unlikely to actually occur, the double checkmates involving pawns have been included.

Two Queens Double Checkmate
Two Rooks Double Checkmate
Two Bishops Double Checkmate
Two Knights Double Checkmate
Two pawns Double Checkmate
Queen-Rook Double Checkmate
Queen-Bishop Double Checkmate
Queen-Knight Double Checkmate
Queen-pawn Double Checkmate
Rook-Bishop Double Checkmate
Rook-Knight Double Checkmate
Rook-pawn Double Checkmate
Bishop-Knight Double Checkmate
Bishop-pawn Double Checkmate
Knight-pawn Double Checkmate

Supported Double Checkmate

A "supported" double checkmate (or assist-mate) is a double checkmate in which at least one of the checking pieces is defended by the other checking piece; this ensures that it cannot be captured by the checked players King.

Two Queens Assist-mate
A Two Queens Double Checkmate where the Queens support each other such that they are directly adjacent to that King and cannot be captured by the King due to the protection they place on each other. This can occur in one of three ways:

The Queens are directly next to each other on adjacent squares.
The Queens are on the same rank or file as each other with a vacant square in between them.
The Queens sit with the enemy King in between them and they support each other via x-ray.

Two Rooks Assist-mate
A double checkmate in which two Rooks, on the same rank or file, place an enemy King in check where at least one of the Rooks is protected from being captured via x-ray protection.

Two Bishops Assist-mate
A double checkmate in which two Bishops on the same diagonal place an enemy King in check where at least one of the Bishops is protected from being captured via x-ray protection.

Queen-Knight Assist-mate
A Queen-Knight double checkmate such that the Queen is directly adjacent to the enemy King and is supported from being captured via the Knights protection.

Single Minor Piece Checkmate
In 4PC it is possible to gain checkmate even when the only (non-King) piece on the board is a Knight or a Bishop. This is because of the multiplicity of Kings that can enable the blocking of squares that a checkmated King would otherwise be able to escape to. As such, there must be at least 3 Kings on the board for this kind of checkmate to play out.

Single Bishop Checkmate
A checkmate in which a singular Bishop is used to check the King whilst the Kings escape squares are blocked by the opponent Kings and edges of the board.

Single Knight Checkmate
A checkmate in which a singular Knight is used to check the King whilst the Kings escape squares are blocked by the opponent Kings and edges of the board.

Teams

4PC Fool's mate
If Red, Yellow and Green all open with their Kings pawn and Blue does not intervene by providing a check on Yellow, then Green becomes checkmated via the fastest possible checkmate possible in 4PC. Red will capture Green's Queen with 2. Qxn8+, and Yellow will then defend Red's queen with 2. -- Bm7#. There are 3568 different combinations of Fool's mate characterised by the moves:

1. (h3, h4) ~ (g12, g11) (l7, k7)
2. QxQn8+ (/Qg13, Qh14, Bh13) Bm7 #

4PC Scholar's mate
Red opens with his Kings pawn, Yellow moves his Queen pawn two steps to h11 and Green also opens with his Kings pawn. Red then captures Greens Queen with 2. Qxn8+, Yellow plays Qh12 and Green must capture the Queen on n8 with his King. Provided Blue does not intervene by checking Yellow at any point or blocking the path of Yellow's Queen on the third move, Yellow can now deliver Scholar's mate with 3. -- Qxn6#.

1. (h3, h4) ~ h11 (l7, k7)
2. QxQn8+ (/Qg13, Bh13) Qh12 KxQn8
3. ~ (/Qxg13, Bh13, QxQh12, Qi11, Qj10, Qk9, Ql8) QxBn6 #

King move mate
A checkmate in which the player right of the checkmated need only move his King in order for the next player to be checkmated.

FFA & Solo

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