Contained within the grid are nine non-overlapping 3x3 regions, which must be located. Each region contains the digits 1-9 once each, so that no digit repeats in any row or column. Cells outside regions don't contain digits. Each region contains a single "doubler" cell, whose value is double its digit for the purpose of cage totals. No row or column contains more than one doubler, and each digit appears in exactly one doubler. Digits may not repeat in a cage, and the sum of cell values in a cage equals the clue in the top left corner of the cage.