Normal sudoku rules apply. Some cells in the grid must be shaded. A digit in a circle indicates the total count of shaded cells in orthogonally connected groups sharing an edge with that cell. Cells with circles cannot themselves be shaded. Every orthogonally connected group of shaded or unshaded cells forms a "killer cage" ie a collection of cells in which no digit may repeat. A cell with a number in its top left corner indicates the sum of the digits in its orthogonally connected group.