Normal sudoku rules apply. Chose two colours with which to colour each cell in the grid such that all cells of either colour are orthogonally connected to each other, and no 2x2 area may be entirely one colour. A circled cell will contain a digit equal to the sum of each connected arrow. Identical digits which see each other by a bishops move (diagonally) must be the same colour. Caged cells must be the same colour.