Futoshiki Puzzle Books - 400 Easy to Master Puzzles 5x5 (Volume 1)

Futoshiki (from Japanese, literally "not equal"; also known as "Hutoshiki", "Unequal") is a logic puzzle.

The puzzle is played on a square grid, such as 5 x 5. The objective is to place the numbers 1 to 5 (or whatever the dimensions are) such that each row, and column contains each of the digits 1 to 5.

Some digits may be given at the start. In addition, inequality constraints are also initially specified 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.