Green Lantern #40 features a Golden Age Green Lantern (Alan Scott) crossover and cover.  It's the first appearance of Krona, Crisis begins, and of course, it contains the origin story of the Guardians.  This book also introduces the Infinite Earths concept!  This is a VERY RARE book in this grade, with only 18 on the CGC census.  This Silver Age key book is graded 9.6 NM+ with off-white to white pages by CGC.  Alignment is nearly perfect and colors are bright with good gloss.