Shape Grammar in Square.

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Rule 1 generates a new square adjacent to an edge of the original square. The rule allows 8 different expansions that, by symmetry, are reduced to 4 different expansions.

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Rule 2 creates a new adjacent square scaled by 2/3 and anchored to the midpoint of one of the edges. This rule allows 8 different expansions. 

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Rule 3 eliminates the square.

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