Onplon is a logic-based number placement puzzle, alternative Sudoku and Solitaire. Starting with a fully completed digit grid, the objective is to clean the grid. Two digits are removed from grid if they are the same or one of them is ten's complement for another and are located in a same row or column in cells so that there aren't another digits between them in horizontal or vertical direction. For example digit 2 is removed with digit 2 or 8. Generation algorithm generates digits so there is always solution.