Normal sudoku rules apply. The dots given in the grid are the centres of (rotationally) symmetric "galaxies" (non-overlapping sets of orthogonally-connected cells), which function as "Region Sum Areas". Cells in Region Sum Areas have an equal sum N within each 3x3 box they visit, and they must visit more than one 3x3 box. Not every cell in the grid has to be part of a galaxy.