2. Clicking on any square that is in the same row or column with the blank square will move every square between the selected square and the blank square.
3. Clicking on any other square (or the blank square) will do nothing.
4. The "Move for me" button will solve the puzzle one move at a time. The strategy for the top two rows is fairly intuitive. The strategy for the bottom two rows is not. The order used is: 13, 9, 14, 10, 11, and 12/15.