A pilot friend of mine introduced me to Sudoku around 2010. He said that pilots, traveling in the passenger seat or staying in hotels abroad, used to play Sudoku to pass the time with something challenging. I knew that Mahjongg could be difficult, but I discovered that Sudoku was no less of a challenge than Mahjongg. Soon, newspapers, journals, and dedicated Sudoku puzzle books flooded the newsstands. A puzzling aspect of Sudoku has always occupied my mind.