George's Secret Key to the Universe is a 2007 children's book written by Lucy and Stephen Hawking with Christophe Galfard. The book was followed by four sequels, George's Cosmic Treasure Hunt in 2009, George and the Big Bang in 2011, George and the Unbreakable Code in 2014 and George and the Blue Moon in 2016. It is intended for readers aged 9 and up. == Synopsis == The main characters in the book are Susan, Ringo, George, Eric, Annie, Dr. Reeper, and Cosmos, the world's most powerful computer. Cosmos can draw windows allowing people to look into outer space, as well as doors which act as portals...

In mathematics, particularly in linear algebra, tensor analysis, and differential geometry, the Levi-Civita symbol represents a collection of numbers; defined from the sign of a permutation of the natural numbers 1, 2, …, n, for some positive integer n. It is named after the Italian mathematician and physicist Tullio Levi-Civita. Other names include the permutation symbol, antisymmetric symbol, or alternating symbol, which refer to its antisymmetric property and definition in terms of permutations. The standard letters to denote the Levi-Civita symbol are the Greek lower case epsilon ε or ϵ, or...