THE theory of aggregates is a very difficult subject, on the border line between mathematics and philosophy, and many questions of the first importance are still unsettled. Indeed, it may be said that the subject is more unsettled now than when Prof. Fraenkel first published his book (1919). In this, the third edition, revised and considerably enlarged, he has endeavoured to give an impartial account of different views, including those of Russell and Whitehead, which until recently have been too little known in Germany. Finally, the author sums up and gives his own personal views, but modestly mentions that these may have to be modified in the near future. Prof. Fraenkel's book appears to be one of the clearest expositions available of an extremely abstract branch of science.
Einleitung in die Mengenlehre.
Von. (Die Grundlehren der mathematischen Wissenschaften in Einzeldarstellungen mit besonderer Berücksichtigung der Anwendungsgebiete, herausgegeben von R. Courant, Band 9.) Dritte umgearbeitete und stark erweiterte Auflage. Pp. xiv + 424. (Berlin: Julius Springer, 1928.) 22.60 gold marks.
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P., H. Einleitung in die Mengenlehre . Nature 124, 8 (1929). https://doi.org/10.1038/124008d0