- → (Ctrl+Z)
Undo your last move, repeatedly if required.
- → (Ctrl+Shift+Z)
Redo a move that was undone, repeatedly if required.
- → (H)
Give a Hint by filling in a vacant square.
Instantly solve the puzzle.
Check an entered puzzle for validity. If it has only one solution, it becomes available for play. If it has no solution or more than one solution, there has probably been an error in the data-entry.