250 Hard Diagonal Futoshiki Challenging Logic Puzzles 4x4.Futoshiki (from Japanese, literally "not equal"; also known as "Hutoshiki", "Unequal") is a logic puzzle. The puzzle is played on a square grid 4 x 4. The objective is to place the numbers 1 to 4 in each row, ensuring that each column also only contains the digits 1 to 4. In some Futoshiki main diagonals also contain the digits 1 through 4. Some digits may be given at the start. In addition, inequality constraints are also initially specifed between some of the squares, such that one must be higher or lower than its neighbour. These constraints must be honoured as the grid is filled out.