Less than: Every domino half in this space must add up to less than the number.
Any point within a given Voronoi region is proximal to the data site (black point) associated with that region.
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Number (2): Everything in this space must add up to 2. The answer is 2-1, placed horizontally; 1-6, placed vertically.
Equal (1): Everything in this space must be equal to 1. The answer is 1-1, placed vertically.