The Challenge The Challenge window gives you the opportunity to try to solve the puzzle yourself, with the program providing some assistance: You can try any arrangement of digits you'd like. The program will automatically enforce the rule requiring that each digit be used only once. The program will do the arithmetic and show you which cells satisfy the rule requiring multiples, and which do not. Color Codes Green: The sum of the digits in the adjoining cells is a multiple. Red: The sum of the digits in the adjoining cells is NOT a multiple. Yellow: The cell, or one or more of its neighbors, is empty. Entering Digits from the Keyboard Select a cell by clicking with the mouse or by pressing the "Tab" key to cycle through the cells. The selected cell will be indicated by a gray border. Type the digit. Only an available digit will be accepted. If the selected cell already contains a digit, it will be returned to the palette. Entering Digits by Clicking Select a cell as in the previous section. Click an available digit in the palette. It's value will be assigned to the selected cell. Dragging Digits Drag a digit from the palette of available digits. The destination will be highlighted with a blue border. Drag a digit from one cell to another. If both cells have values, they will trade places. Drag a digit out of a cell, either back to the palette, or simply to the area surrounding the puzzle.