Divide the grid into 8 regions, each consisting of 8 orthogonally-connected cells. Regions may wrap around the grid's edges, both horizontally and vertically. Each row, column, and region contains the digits 1 to 8 exactly once. Some region boundaries are given and have to be respected. The digits along an arrow sum to the digit in its circle. The digits 1 to 3 are small and the digits 6 to 8 are large. Any two orthogonally adjacent cells separated by a region border must contain one small and one large digit. This includes cells in different regions at opposite edges of the grid, since the grid wraps.
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