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The Gatekeepers

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This post was released for Issue 19 of Bitcoin Magazine as part of a series of  articles about puzzles and games that started with Issue 12.

This series of puzzles and games was inspired by a talk given by the founder of the Pirate Party, Rick Falkvinge, at the European Bitcoin Conference in Prague on November 26, 2011 called ‘the fall of the gatekeepers’. A gatekeeper is a person who controls access to something, for example via a city gate. In the late 20th century the term came into metaphorical use, referring to individuals who decide whether a given message will be distributed by a mass medium. In his talk, Falkvinge maps the epic history of the people’s thirst for knowledge and communication versus the ruling classes’ attempts to control them and links this concept to Bitcoin and how it will bring the banking establishment to its knees.

THE HOARDER AND THE GATEKEEPER

The Hoarder and the Gatekeeper is a game for 2 players (the Hoarder and the Gatekeeper) that can be played on a hexagonal grid of any size. We’ll use a grid of 4 hexes per side here and we’ll call it ‘Coinland’.

Coinland is full of coins, one coin per cell with the exception of the central one. Each cell is connected to its neighbouring cells by an edge. The ‘Hoarder’ will try to collect as many coins as possible by moving from cell to cell, while the Gatekeeper will try to collect coins by ‘taxing’ the Hoarder, placing gates on the edges between cells and charging a fee each time the Hoarder crosses them.

Print the board above (or draw one yourself). Then use loose change or draughts pieces or beans or whatever to fill the cells. Keep the centre cell empty.

The Hoarder uses a chess pawn (or any other object that fits inside a cell). The Gatekeeper uses a marker of a different colour than the edges of the board (if possible). Place the Hoarder piece in the centre cell.

Starting with the Gatekeeper, players alternate turns during the game until all coins have been collected or the Hoarder is not able to move, whatever happens first.

On her turn, the Gatekeeper must draw a gate in any edge between 2 cells.

And on her turn, the Hoarder must move her piece in a straight line to a non-empty cell (it must contain a coin) in any of the 6 directions. She must pay as many coins to the Gatekeeper as gates she crossed during the move (she cannot move if she doesn’t have coins enough to pay). If there is a coin on the landing cell then the Hoarder collects it.

The Hoarder pays 2 coins and collects 1 coin.

When the game ends, count the coins that the Hoarder has managed to keep. This is her score. Then reverse roles and play again. Whoever achieved the highest score playing as the Hoarder wins.

PUZZLE

Coinland is full of gates and the gatekeeper is asleep (so only the Hoarder plays this time). Find a sequence of moves that harvest the most coins. Remember that the destination cell for each move must contain a coin, and each time you cross a gate you must pay one coin as a fee!

RACE FOR THE COINS

In this game both players are hoarders and gatekeepers at the same time. So both need a pawn of a different colour and a marker of the same colour as their pawn. Setup the board as show in the figure. There will be 3 cells without coins.

Decide the starting player by any peaceful means. Players alternate turns during the game until all coins have been collected or both players pass in succession.

On your turn you must do one and only one of these actions:

• Move your Hoarder according to the rules (destination must have a coin). For every gate of the opponent’s colour that is crosses you pay 1 coin to her. It is not allowed to move your Hoarder across the other hoarder.

• Draw a gate of your colour on an empty edge.

• Pass if you cannot make a valid move (either moving your Hoarder or drawing a gate).

The player with more coins when the game ends wins.

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