I see the square grid as playboard, where the smallest square is the unit of real track pieces. For instance, the straight piece takes 1x8 inches, curve takes 8x8 inches, it defines 1x1 inch square as the unit. (I guess that all real pieces have this character.) One square on the playboard can be occupied by 1 piece, maximally. Every piece has 2 or more endpoints. The endpoints are the edges of occupied square units. When some piece is put on the playground, the sum of not coupled endpoints is recalculated. The goal is sum == 0.
Update: the sum of endpoints -> the sum of not coupled endpoints

In reply to Re: Closed geometry: a train track problem by pajout
in thread Closed geometry: a train track problem by SamCG

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