Normal sudoku rules apply. Shade some cells so that all shaded cells are orthogonally connected, and all unshaded cells are orthogonally connected. No 2x2 region can be completely shaded or unshaded. Each cell in one region has a value of its digit plus 1. Each cell in the other region has a value of its digit minus 1. The sum of the values of cells on lines connecting two circles is equal to a concatenation of the two values in the circles, in some order. For example, 3_346_1 is valid, as 3+4+6=13. Leading zeros are allowed. Every line between two circles is summed separately.