Kei-Yen

**Kei-Yen** () is an indoor Meitei traditional game, often compared to chess due to its strategic nature. The game derives its name from the Meitei language words "Kei," meaning Tiger, and "Yen," meaning Rooster or Cock. Its origins are linked to Meitei mythology. The game involves two players, each controlling different pieces, and is played on a board with specific logical lines that guide the movement of the pieces.

Kei-Yen is typically played with 25 Yen pieces and 2 Kei pieces. The game begins with a toss to determine which player controls Kei and which controls Yen. The player with Kei pieces moves first. The objective of the Kei player is to eliminate all Yen pieces, while the Yen player aims to block the movements of Kei. The game ends when either the Kei player captures all the Yen pieces or the Yen player successfully blocks all Kei movements, ensuring a definitive winner.

Historically, the game was played with sticks to represent the pieces on a board or ground marked with lines to define movement. The game is known for its ability to enhance strategic thinking and logical planning. It can be played by both men and women, and there are various strategies to master the game.

## Mythology

Kei Yen Sanaba () is a Meitei traditional game rooted in the cosmogony of the Meitei people. It narrates the mythological conflict between Ashiba (God Sanamahi) and his younger brother, Konjin Tuthokpa (God Pakhangba). According to the legend, Ashiba returned home after completing Nongkhong Koiba—a mythical journey symbolizing the sailing of the universe seven times. Upon his return, he discovered that Konjin had taken their father’s throne.

Konjin’s inability to perform the same cosmic journey as Ashiba led to tension. Their mother, Leimarel Sidabi, out of compassion for Konjin, advised him to pray to their father, Sidaba, and to walk around his throne. She explained that their father and his throne represented the origin of the universe.

As Ashiba grew enraged and sought to attack Konjin, the Lainura Taret, a group of seven female deities, intervened. They surrounded Konjin and sang a song to pacify Ashiba’s anger:

In this song, “Ke” (Tiger) symbolizes God Sanamahi, while “Yen” (Hen) represents God Pakhangba. The game conveys a moral lesson about the supremacy of the mind over emotions. This song is also performed during Ougri Hangel Chongba, a ritual dance associated with the Lai Haraoba festival.

## Kei-Yen Board

The Kei-Yen board is a two-dimensional square grid with 5 × 5 (25) positions, providing spaces for movement of both Kei and Yen pieces. One player controls two Kei pieces, represented by small wooden sticks, while the opposing player controls 25 Yen pieces, which are smaller wooden sticks to differentiate them from the Kei pieces.

Movement on the board is restricted to the dark spaces along the lines. The Kei pieces move across two dark spaces, located at the midpoints of either the farthest right and left sides or the topmost and bottommost sides of the board. The Yen pieces, on the other hand, move across four dark spaces. Yen pieces are grouped into four sets, each beginning at a specific position: the second dark space from the leftmost and topmost, the rightmost and topmost, the leftmost and bottommost, and the rightmost and bottommost positions.

## Opening Phase of Kei-Yen

In the game of Kei-Yen (), Kei is the stronger piece, represented by two larger sticks. Its objective is to capture the Yen pieces by crossing over them along the lines on the board. Each time a Kei piece crosses a Yen piece or a group of Yen pieces, it captures one Yen, reducing the number of Yen pieces. Depending on the available moves, a Kei piece may capture one or more Yen pieces in a single move. The Kei player wins by capturing all the Yen pieces.

Yen, in contrast, is the weaker piece, consisting of 25 smaller sticks. Yen cannot capture Kei pieces and must focus on defense. Its goal is to block the movement of the Kei pieces. The Yen player wins only if both Kei pieces are successfully blocked from further movement.

## Strategy and Tactics

The strategy in Kei-Yen involves achieving long-term positional advantages to secure victory. The Kei player aims to position their pieces in a way that maximizes the potential to capture Yen pieces with each move. The key is to create opportunities for capturing Yen while maintaining flexibility in response to the evolving game.

For the Yen player, the strategy focuses on evading capture and blocking the movement of the Kei pieces. Yen's moves should be aimed at protecting its pieces and restricting the options of the Kei player, ultimately preventing the Kei from capturing all Yen pieces.

In Kei-Yen, strategy and tactics are closely intertwined. Strategic objectives are generally realized through tactical moves, while tactical opportunities depend on the positions established through earlier strategic decisions. Success in the game requires a balance between long-term planning and the ability to take advantage of immediate opportunities.

## Fundamentals of Tactics

In Kei-Yen, tactics focus on short-term moves that influence subsequent actions. These short-term tactics aim to advance a player's position and manipulate the following moves. The complexity of winning depends on the player’s ability to calculate and implement strategic decisions.

In positions with many possible moves for both players, deep calculations and long-term strategies may be challenging and less practical. However, in tactical positions with limited possible variations, skilled players can plan and calculate longer sequences of moves.

Simple one- or two-move tactical actions, such as threats, exchanges, and double attacks, can be combined into more complex combinations. These tactical sequences are often determined by the game’s position, with certain moves being forced by the circumstances of the match.

## Fundamentals of Strategy

Kei-Yen strategy involves the evaluation of positions on the board and the formulation of long-term plans aimed at winning the game. During this evaluation, players consider various factors, such as the positioning of pieces, control of the center, centralization, and the overall structure of the pieces. Additionally, players assess offensive and defensive strategies, the control of key opponent moves, and potential attack sequences.

Strategic considerations include the movement patterns of pieces, such as diagonal or linear moves, and identifying positions for both attacking and evading capture. Effective strategy in Kei-Yen requires careful planning and the ability to anticipate and respond to the opponent’s tactics over multiple moves.

## Evaluation of Position

The primary step in evaluating a position in Kei-Yen is to assess the advantages of each player, which involves counting the potential moves and opportunities available to both. Strategy in the game is influenced by prior experience and the assessment of the opponent’s moves. Kei, having only one move per turn, either to capture a Yen or occupy a more advantageous position, generally aims to control positions that offer multiple opportunities for capturing Yen or progressing to a better position in subsequent moves. While Kei does not face direct threats of being eliminated, it must be cautious of becoming trapped by the Yen pieces in future moves.

The strategy for Yen is distinct, focusing on occupying positions that ensure survival and provide opportunities to counteract Kei’s moves. Yen pieces should move in coordination, with each move being influenced by the positions of other Yen pieces. Kei’s strategy, in contrast, aims to disrupt the coordinated movement of Yen, breaking up their groups to make them easier to capture. This dynamic reflects a predator-prey model, with both players utilizing strategic thinking to gain an advantage.

## Phases

The game of Kei-Yen consists of three distinct phases: the opening phase, the middle game phase, and the end game phase. Each phase represents a different stage of the match.

### Opening Phase

The opening phase begins with the initial placement of the pieces. Four groups of Yen are positioned at specific locations on the board, each group containing five Yen pieces. The two Kei pieces are placed separately, typically at the center of either the farthest right and left sides or the topmost and bottommost sides of the board. This phase establishes the starting positions for both players as they prepare for the subsequent moves.

### Middle Game Phase

In the middle game phase of Kei-Yen, the game progresses with alternating turns, beginning with the Kei player. Kei aims to capture all the Yen pieces, while Yen’s goal is to block the movement of Kei pieces and prevent them from advancing. Both players utilize all available tactics during this phase, focusing on positioning, strategy, and responding to the opponent’s actions.

### End Game Phase

The Kei-Yen game guarantees a winner, as there are no draws. The game can end in one of two ways: either a "finish by Kei" or a "finish by Yen."

#### Finish by Kei

Kei wins by either capturing all the Yen pieces or reaching a point where the remaining Yen pieces can no longer block Kei’s movements, making further progression inevitable.

#### Finish by Yen

Yen wins by successfully blocking all possible moves of the Kei pieces, rendering them immobile and preventing further action by Kei.

## Arrange Move

An arrange move refers to the action of shifting a piece from its current position to a more advantageous position on the board, either by Kei or Yen pieces. Both Kei and Yen have specific conditions that govern their moves, with Kei having an additional move compared to Yen.

### Kei and Yen Arrange Move

In Kei-Yen, the purpose of arranging moves differs between the two players. The Kei player arranges its pieces to secure positions that facilitate capturing Yen pieces, while the Yen player arranges its pieces to block the movement of Kei and prevent it from advancing. In this phase, players evaluate their current positions and aim to move their pieces to more favorable locations during their respective turns.

### Condition Check for Arrangement Move

In the Kei-Yen game, the condition check for arrangement moves can be represented using a two-dimensional array, a(m, n), where m and n range from 0 to 4. The array a(m, n) corresponds to a specific position on the Kei-Yen board, with m and n indicating the row and column of that position. This representation allows for systematic evaluation of potential moves and their validity during the game.

There are three primary conditions that players must consider when making arrangement moves:

- Same Position Check Condition

- Even-Odd Condition

- Odd-Even Condition

These conditions are used to assess the legality and strategic value of a move, and are explained in detail through algorithms and pseudo-code in later sections.

Additionally, it is important to consider moves related to extreme end positions. Two types of extreme end position cases exist for common moves. The following describes the logical moves and their corresponding pseudo-code:

#### Properties of Move C1

When a(m, n) is at an "even-even" extreme end position (where m ≠ n, m ≠ n + 4, and m + 4 ≠ n), the position a(m, n) has five possible moves. The number of valid moves is determined by the structure of the board and the location of the pieces at this particular position.

In the Kei-Yen game, a(m, n) represents a position on the game board, where m and n are the row and column indices, respectively. The notation a(m, n) is used to denote specific positions and the moves that can be made from them.

The following examples describe possible moves from a given position:

1. a(m-1, n+1), a(m-1, n), a(m+1, n), a(m+1, n+1), a(m, n+1)

This sequence of moves refers to the possible positions that a piece can move to from a(2, 0). The corresponding moves are:
   - a(1,1)
   - a(1,0)
   - a(3,0)
   - a(3,1)
   - a(2,1)

2. a(m-1, n+1), a(m-1, n), a(m-1, n-1), a(m, n-1), a(m+1, n+1)

This sequence of moves refers to the possible positions that a piece can move to from a(4, 2). The corresponding moves are:
   - a(3,3)
   - a(3,2)
   - a(3,1)
   - a(4,1)
   - a(5,3)

These move sequences define the potential positions a piece can occupy, depending on its current location on the board. The notation is used to specify the allowed movements and is essential for evaluating the arrangement of pieces in the game.

#### Properties of Move C2

Move C2 pertains to positions on the Kei-Yen board where the coordinates are at extreme ends and follow certain parity conditions:

Even-Odd or Odd-Even Positions: These are positions where m is an even number and n is an odd number, or vice versa.

Even-Even Positions: These are positions where both m and n are even numbers.

For these positions, both Kei and Yen have three possible moves, as defined by the following conditions:

- a(m, n+1), a(m, n-1), a(m+1, n)
This is applicable when m = 0 and n = 1 or n = 3.

- a(m-1, n), a(m+1, n), a(m, n+1)
This applies when m = 1 or 3, and n = 0.

- a(m-1, n), a(m, n-1), a(m+1, n)
This applies when m = 1 or 3, and n = 4.

- a(m-1, n), a(m-1, n-1), a(m, n-1)
This applies when m = 4, and n = 1 or 3.

- a(m, n+1), a(m+1, n), a(m+1, n+1)
This applies when m = 0, and n = 0.

- a(m-1, n), a(m-1, n-1), a(m, n-1)
This applies when m = 4, and n = 4.

#### Properties of Move C3

Move C3 pertains to positions along the main diagonal of the Kei-Yen board that are not located at the extreme ends. These positions occur when both m and n are equal but are not at the extreme points, such as (0, 0), (4, 4), (0, 4), or (4, 0).

In these positions, each piece has eight possible moves, as the movement is more flexible compared to the extreme positions. Specifically, for m = 1, 2, or 3 and n = 1, 2, or 3, excluding the extreme diagonal positions (1, 3) and (3, 1), players have multiple movement options in all directions along the board.

#### Pseudo Code for C3 Logic

The sequence of moves associated with C3 logic is as follows:
1. Move to the position `a(m, n+1)`.
2. Transition to `a(m−1, n+1)`.
3. Repeat the move to `a(m−1, n+1)`.
4. Move to the position `a(m, n−1)`.
5. Proceed to `a(m+1, n−1)`.
6. Transition to `a(m+1, n)`.
7. Move to the position `a(m+1, n+1)`.
8. Finally, return to `a(m, n+1)`.

#### Properties of Move C4

This move applies when the element `a(m, n)` is neither located on the main diagonal nor positioned at an extreme endpoint. Under these conditions, four possible movements exist:
- For `m = 1` and `n = 1 or 3`.
- For `m = 3` and `n = 1 or 3`.
- For `n = 1` as an individual case.

#### Pseudo Code for C4 Logic

The moves for C4 logic are structured as follows:
1. Transition to the position `a(m−1, n)`.
2. Move to `a(m, n+1)`.
3. Proceed to `a(m+1, n)`.
4. Conclude with a move back to `a(m, n+1)`.

#### Property of Move B1

Move B1 is characterized by three distinct sub-properties:
1. Property of Move A1: This examines whether the current position remains unchanged, often termed the "Same Position Check Condition."
2. Property of Move A2: This validates whether there is alternation between even and odd positions, referred to as the "Even-Odd Check Condition."
3. Property of Move A3: This evaluates the alternation between odd and even positions, known as the "Odd-Even Check Condition."

Move B1 is primarily utilized by Kei to systematically organize and arrange their movements.

### Same Position Check Condition

This condition applies to cases where m equals n, and both m and n are either even numbers, odd numbers, or identical values.

#### Property of Move A1

For a position a(m, n), where m and n meet the criteria (m equals n as an even number, m equals n as an odd number, or identical values with m greater than or equal to zero and n less than or equal to four), the possible movements include:
1. a(m−1, n+1)
2. a(m−1, n)
3. a(m−1, n−1)
4. a(m, n−1)
5. a(m+1, n−1)
6. a(m+1, n)
7. a(m+1, n+1)
8. a(m, n+1)

Kei and Yen can move freely from the current position to any adjacent location, provided there is sufficient space available for movement.

#### Pseudo Code of A1 Logic

For a(m, n), if n is an even or odd number or m equals n (identical number):

1. Position at Same Number
   - When m equals n as an even number or m equals n as an odd number and the position is not at an extreme endpoint, there are eight movement options using the properties of move C3.
   - If positioned at an extreme corner and m equals n where m equals n plus four, m plus four equals n, or m equals n (both being even numbers), three movement options are available using the properties of move C2.

2. Position at Extreme Endpoint (Non-Corner)
   - If positioned at an extreme endpoint where m equals n plus two or m plus two equals n (both being even numbers), five movement options are available using the properties of move C1.

##### Example

Consider the current position at a(2, 2) where m equals 2 and n equals 2. The possible movements using the properties of move C3 are:
1. a(1, 3) through a(m−1, n+1)
2. a(1, 2) through a(m−1, n)
3. a(1, 1) through a(m−1, n−1)
4. a(2, 3) through a(m, n+1)
5. a(3, 1) through a(m+1, n−1)
6. a(3, 2) through a(m+1, n)
7. a(3, 3) through a(m+1, n+1)
8. a(2, 3) through a(m, n+1)

### Even-Odd Check Condition

This condition applies to cases where the value of m is an even number and the value of n is an odd number. The position `(m, n)` represents the location of Kei or Yen, with m as an even number and n as an odd number.

#### Property to Move A2

For the position a(m, n), where m is an even number and n is an odd number (with m greater than or equal to zero and n less than or equal to four), the following moves are available:
1. a(m−1, n+1), a(m, n−1), a(m+1, n), a(m, n+1) when m equals 2 and n equals 1 or 3.
2. a(m, n−1), a(m+1, n+1), a(m, n+1) when m equals 0 and n equals 1 or 3.
3. a(m−1, n), a(m, n−1), a(m, n+1) when m equals 4 and n equals 1 or 3.

#### Pseudo Code of A2 Logic

For the position a(m, n), if m is an even number and n is an odd number:
1. When a(m, n) is not at an extreme position (i.e., m equals 2 and n equals 1 or 3), the position has four possible moves using the properties of move C4.
2. When a(m, n) is at an extreme position (i.e., m equals 0 or 4 and n equals 1 or 3, respectively), the position has three possible moves using the properties of move C2.

### Odd-Even Check Condition

This condition applies to cases where m is an odd number and n is an even number.

#### Property to Move A3

For the position a(m, n), where m is an odd number or n is an even number (with m greater than or equal to zero and n less than or equal to four), the following moves are available:
1. a(m−1, n), a(m, n−1), a(m+1, n), a(m, n+1) when m equals 1 or 3 and n equals 2.
2. a(m−1, n), a(m+1, n), a(m, n+1) when m equals 1 or 3 and n equals 0.
3. a(m−1, n), a(m, n−1), a(m+1, n) when m equals 1 or 3 and n equals 4.

#### Pseudo Code of A3 Logic

For the position a(m, n), if m is an odd number and n is an even number:
1. When a(m, n) is not at an extreme position (i.e., m equals 1 or 3 and n equals 2), the position has four possible moves using the properties of move C4.
2. When a(m, n) is at an extreme position (i.e., m equals 1 or 3 and n equals 0 or 4, respectively), the position has three possible moves using the properties of move C2.

## Condition Check for Killing Move (Kei Move)

The condition check for the killing move pertains to the Kei's ability to transition from one position to another to eliminate the Yen. This move incorporates specific conditions that extend beyond those applicable to standard Yen movements.

Kei is capable of executing a killing move when the following requirements are met:

1. The position adjacent to Yen is unoccupied.

2. Kei and Yen are aligned on the same row, column, or diagonal on the Kei-Yen board.

The conditions for alignment and movement depend on the following criteria:

1. Even-Odd Check Condition: Alignment occurs when the coordinates of Kei exhibit an even-odd numerical relationship.

2. Same Position Check Condition: Alignment occurs when Kei's coordinates are identical or match the same-number criteria.

3. Odd-Even Check Condition: Alignment occurs when the coordinates of Kei demonstrate an odd-even numerical relationship.

The killing move is permissible only if these stipulated conditions are satisfied and the positional arrangement on the board allows such an action. These conditions ensure that the move adheres to strategic rules and is performed within the established framework of the game.

## Same Position Check Condition for Killing Moves

This condition applies when the coordinates m and n are either both even, both odd, or identical. Here, m and n denote the indices of the first and second positions in the array "a". The condition is met when m equals n, which may represent either even numbers, odd numbers, or the same value.

### Property to Move B2

For a position a(m, n), where m and n are either both even, both odd, or identical values with m greater than or equal to zero and n less than or equal to four, the possible moves range from two to eight positions. These moves include:
1. a(m−2, n+2)
2. a(m−2, n)
3. a(m−2, n−2)
4. a(m, n−2)
5. a(m+2, n−2)
6. a(m+2, n)
7. a(m+2, n+2)
8. a(m, n+2)

### Pseudo Code of B2 Logic

For the position a(m, n), if n is an even number, odd number, or m equals n:

1. When m equals n and both equal 2, there are eight possible moves to capture Yen: a(m−2, n+2), a(m−2, n), a(m−2, n−2), a(m, n−2), a(m+2, n−2), a(m+2, n), a(m+2, n+2), and a(m, n+2).
2. When m equals n and both equal 0, there are three possible moves: a(m, n+2), a(m+2, n+2), and a(m+2, n).
3. When m equals n and both equal 1, there are three possible moves: a(m, n+2), a(m+2, n+2), and a(m+2, n).
4. When m equals n and both equal 3, there are three possible moves: a(m−2, n), a(m−2, n−2), and a(m, n−2).
5. When m equals n and both equal 4, there are three possible moves: a(m−2, n), a(m−2, n−2), and a(m, n−2).
6. For even positions where m equals n but not equal to 2, and m does not equal n:
   - At m equals 0 and n equals 4, the moves are a(m, n−2), a(m−2, n−2), and a(m, n+2).
   - At m equals 0 and n equals 0, the moves are a(m, n+2), a(m+2, n+2), and a(m+2, n).
   - At m equals 4 and n equals 0, the moves are a(m−2, n+2), a(m−2, n), and a(m, n+2).
   - At m equals 4 and n equals 4, the moves are a(m−2, n), a(m−2, n−2), and a(m, n−2).
7. For even positions where m equals n+2 or m+2 equals n, and m does not equal n:
   - At m equals 0 and n equals 2, the moves are a(m, n−2), a(m+2, n−2), a(m+2, n), a(m+2, n+2), and a(m, n+2).
   - At m equals 2 and n equals 0, the moves are a(m−2, n), a(m+2, n), a(m+2, n+2), a(m, n+2), and a(m−2, n+2).
   - At m equals 4 and n equals 2, the moves are a(m−2, n), a(m−2, n−2), a(m, n−2), a(m, n+2), and a(m−2, n+2).
   - At m equals 2 and n equals 4, the moves are a(m−2, n), a(m−2, n−2), a(m, n+2), a(m+2, n−2), and a(m+2, n).
8. For odd positions where m equals 1 and n equals 3 (or vice versa):
   - At m equals 1 and n equals 3, the moves are a(m, n−2), a(m+2, n−2), and a(m+2, n).
   - At m equals 3 and n equals 1, the moves are a(m−2, n+2), a(m−2, n), and a(m, n+2).

### Even-Odd Condition for Killing Moves

This condition applies to cases where m is an even number and n is an odd number.

#### Property to Move B3

For a position a(m, n), where m is an even number and n is an odd number (with m greater than or equal to zero and n less than or equal to four), the possible moves are limited to two positions. These moves include:
1. a(m, n−2) and a(m, n+2) for m equals 0 or 2 and n equals 1 or 3, provided m does not equal 4.
2. a(m−2, n) and a(m, n−2) for m equals 4 and n equals 1 or 3.

#### Pseudo Code of B3 Logic

For a position a(m, n), if m is an even number and n is an odd number:

1. When m does not equal 4, the position has two possible moves: a(m, n−2) and a(m, n+2).
2. When m equals 4 and n equals 1 or 3, the position has two possible moves: a(m−2, n) and a(m, n−2).

## Odd-Even Condition

The odd-even condition applies when m is an odd number and n is an even number. In this scenario, m and n represent the indices of the first and second positions within the array "a." This condition is characterized by m being odd and n being even.

### Property to Move B4

For a position a(m, n), where m is an odd number and n is an even number (with m greater than or equal to zero and n less than or equal to four), the piece can move up to two positions. The possible movements are:
1. a(m+2, n+2) and a(m, n+2), applicable when m equals 1 and n equals 0, 2, or 4.
2. a(m−2, n) and a(m, n−2), applicable when m equals 3 and n equals 0, 2, or 4.

### Pseudo Code of B4 Logic

For a position a(m, n), if m is an odd number and n is an even number:

1. When m equals 1 and n equals 0, 2, or 4, the position has two possible moves: a(m+2, n+2) and a(m, n+2).
2. When m equals 3 and n equals 0, 2, or 4, the position has two possible moves: a(m−2, n) and a(m, n−2).

## In popular culture

Ningtamba Designs (ND), a fashion and design start-up based in Imphal, introduced its first collection, featuring winter wear for women. The collection is titled 'Kei-Yen,' named after a traditional Meitei board game of the same name.

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