A third example of pattern recognition used for problem solving is more recent. Around 2007, an art collector purchased this chalk on vellum (animal skin) drawing of a young girl. He boldly suspected that the artwork could be attributed to Leonardo Da Vinci, painter of the Mona Lisa and The Last Supper. Experts from the art world got involved and started looking for patterns--features of the piece that were consistent with known Da Vinci style, as well as other scientific and historic clues that might mean it was a Da Vinci work. Through their investigation they found a long list of evidence (enough to publish a book on the topic) that the drawing was in fact created by Da Vinci.