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Figure 4
Arrows on the edges of the outer hexagon which are oriented in the counter-clockwise direction are represented by short red half-diameters. For arrows in the clockwise orientation we use short blue half-diameters. If we include the striping decoration of the inner hexagons as well (Fig. 3[link]), we arrive at the fully decorated double hexagons shown on the right-hand side of the figure. Evidently the decorated tiles carry information fully equivalent to the arrowing. Notice that proper matching of the edges of outer hexagons is equivalent to a change of color as the short diagonal passes through the common edge. Also notice that if one holds the black stripe horizontally, then as one moves along a full blue diagonal from right to left, the diagonal passes through the black stripe from above to below. It is the other way around for red stripes. We use this observation to make the color determination of the short diagonals in Fig. 10[link].

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ISSN: 2053-2733
Volume 73| Part 3| May 2017| Pages 246-256
https://doi.org/10.1107/S2053273317003576
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