Mind Ninja Pattern: Havannah

Either a fork, a bridge or a loop of red stones and, at the same time, none of those structures in grey. The structures may be embedded.

A fork is a chain linking any three sides. Corners do not belong to sides.

A bridge is a chain linking any two corners.

A ring is a chain around at least one cell. The cell(s) inside the loop can be empty or occupied by any color.

Examples (from left to right: a red fork, a red bridge, and a red loop):


This is almost identical to the connection game by the same name, invented by Christian Freeling (see here and here). The only difference is that while there is a small possibility for a draw in the original game, there is none here (here, the blocker wins in those cases which would be drawn in the original game).

I put this in the initial tournament list first because Havannah is a great game, but also to illustrate two important methods for specifying patterns.

First, a pattern can be defined as a combination of other patterns related by logical operators (AND, OR, NOT, XOR, etc). In this case, the builder has the choice of building a red fork OR a red bridge OR a red loop.

Second, a pattern can be defined by what it is NOT or CANNOT contain (this is just another kind of logical operation, but it's worth emphasizing, because new players often fail to recognize that patterns can be defined this way). In this case, the builder's pattern cannot contain a grey fork, bridge, or loop. Defining patterns in the negative this way effectively turns the blocker into a builder. For example, in this case, the blocker can try to build a fork, bridge, or loop in grey.

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