 The second edition was eventually completed by two colleagues, Fred Klein and Ronald Dean Nolen, and released in 1994.Klein and Nolen continued to revise and update Katz's work as needed, with a 3rd edition released in 1998; a 4th edition in 2001, and a 5th edition in 2005.Nolen alone revised and issued a 6th edition of Katz's work, published in 2008.