“Sudoku has furrowed the brows of a generation of commuters, but will it be replaced by a new puzzle from Japan? …Like sudoku, the smaller kenken consists of a numbers square where the figures cannot be duplicated within rows and columns.

But with the new puzzle, there’s the added dimension of having to reach certain target numbers inside smaller blocks by adding, subtracting, multiplying or dividing the numerals in the cells within…” (BBC)