A tessellation is a way of covering a plane with a repeating pattern... Basically, it's like creating wallpaper. In 1975, Marjorie Rice (1923- 2017), a mother and amateur mathematician, read an article by Martin Gardner in Scientific American that listed ALL possible "pentagonal tessellations" in the plane. A mathematician had just proved that the list was complete. Except that Marjorie, working alone at home, found 4 new ones... The theorem was wrong!