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Suppose I have a regular grid of identical hexagons that tile the plane, that is a hexagonal lattice.

How can I determine if a connected subset of these hexagons (i.e. a poly-hex) can tile the plane by translations that form a (Bravais) lattice? For reference, here is a picture:

enter image description here

The four shapes on the right can tile the plane, while the left-most shape cannot.

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You mean just translations, no rotations allowed? That may be decidable. – Will Jagy Mar 12 '13 at 4:14
That is correct, only translations, and no rotations. Not only that, but the overall tiling should be periodic. – Victor Liu Mar 12 '13 at 5:01
The polyhexes that tile by translation, up to order 9, can be found by links from --- e.g., there are 6572 polyhexes of order 9, of which only 387 tile by translation. There are also references there to the literature. See also – Gerry Myerson Mar 12 '13 at 5:04

John Conway obtained an algorithm for deciding (a particular case of) the tiling problem with polyminoes and polyhexes.

Such algorithm is explained by Thurston here.

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