ADDER'S COIL - HOW TO PLAY: Make a single path through all squares of the grid formed by the numbers 1 to 9 in order, repeated as many times as necessary. After 9 is reached, begin again at 1.

                 
                 
                 
                 
                 
                 
                 
                 
                 
                 


The correct path - the Adder's Coil - tracks through adjacent squares, horizontally or vertically - but not diagonally. It forms a continuous loop that does not cross itself, split or reach a dead-end at any point.

                 
                 
                 
                 
                 
                 
                 
                 
                 
                 

1. To enter a number, first select a player square.

2. To show the path between adjacent 'given' numbers, select one of the given numbers.

3. More clues are available for easier puzzles than for harder ones.

4. Only one puzzle can be saved at a time. A previously saved puzzle is overwritten.