Lessells, D. VanNostrandCompany, 1925 Vibration Problems in Engineering, D. VanNostrandCompany, 1st Ed. 1928, 2nd Ed. 1937, 3rd Ed. 1955 (with D. H. Young)
{\displaystyle c\leq \varphi (B)<\infty } Halmos, Paul R., Measure Theory, D. VanNostrandCompany, Inc., 1950, pp. 58. A. N. Kolmogorov & S. V. Fomin, translated