books.google.com - In the nineteenth century, French mathematician Evariste Galois developed the Galois theory of groups-one of the most penetrating concepts in modem mathematics. The elements of the theory are clearly presented in this second, revised edition of a volume of lectures delivered by noted mathematician Emil...http://books.google.com/books/about/Galois_Theory.html?id=kVuYGdGizHEC&q=Lemma&utm_source=gb-gplus-shareGalois Theory