Trace Numbers #68
Draw as many lines in the grid as there are cells with the number 1. The individual sections of the lines run horizontally or vertically between the centres of orthogonally adjacent cells.
A line starts in a cell with a 1, then passes in sequence through cells with the numbers 2, 3, etc., and ends in a cell with the highest occurring number. Exactly one line must pass through each cell (i.e., the lines must not cross themselves or each other).