 There is also lack of agreement over the importance of the second edition of the book, which appeared in 1925 (Volume I) and (Volumes II and III were directly reprinted from the first edition in 1927). The revisions were done by Russell, although Whitehead was given the opportunity to advise. In addition to the correction of minor errors throughout the original text, changes to the new edition included a new Introduction and three new appendices. (The appendices discuss the theory of quantification, mathematical induction and the axiom of reducibility, and the principle of extensionality respectively.) The book itself was reset more compactly, making page references to the first edition obsolete. Russell continued to make corrections as late as 1949 for the 1950 printing, the year he and Whitehead's widow finally began to receive royalties.