Normal sudoku rules apply. Divide the entire grid into killer cages, each of which is a set of orthogonally connected cells. Each cage contains exactly one clue, which may be in any position in the cage, and gives the sum of the digits in that cage. Digits may not repeat in a cage. Single cell cages are allowed. Draw a single loop through the centres of some cells with no branches or crossings, which visits each cage exactly once. The loop moves orthogonally from cell to cell. If two cells share an edge but are in different cages, at least one of them must be visited by the loop. The digit in a clued cell equals the number of cells in that cage which are visited by the loop.