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Note the first row (marked with red). The first two triangles are different, therefore they can be beside each other in the puzzle. However, the 2nd and 3rd triangle are the same. They must be separated by at least one background square. The 3rd and 4th triangles are different. They can be side-by-side also.
In the last row (marked with green), the triangles are the same. They must be separated by at least one background square. |