The second part follows the approach of Riesz and Nagy in which the Lebesgue integral is developed without the need for any measure theory. Our approach is novel in part because it uses integrals of continuous functions rather than integrals of step functions as its starting point. This is natural because Riemann integrals of continuous functions occur much more frequently than do integrals of step functions as a precursor to Lebesgue integration. In addition, the approach used here is natural because step functions play no role in the novel development of the Riemann integral in the first part of the book. Our presentation of the Riesz-Nagy approach is significantly more accessible, especially in its discussion of the two key lemmas upon which the approach critically depends, and is more concise than other treatments.
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Ronald B. Guenther is an emeritus professor in the Department of Mathematics at Oregon State University. His career began at the Marathon Oil Company where he served as an advanced research mathematician at its Denver Research Center. Most of his career was spent at Oregon State University, with visiting professorships at the Universities of Hamburg and Augsburg, and appointments at research laboratories in the United States and Canada, and at the Hahn-Meitner and Weierstrass Institutes in Berlin. His research interests include mathematically modeling deterministic systems and the ordinary and partial differential equations that arise from these models.
John W. Lee is an Emeritus Professor in the Department of Mathematics at Oregon State University, where he spent his entire career with sabbatical leaves at Colorado State University, Montana State University, and many visits as a guest of Andrzej Granas at the University of Montreal. His research interests include topological methods use to study nonlinear differential and integral equations, oscillatory properties of problems of Sturm-Liouville type and related approximation theory, and various aspects of functional analysis and real analysis, especially measure and integration.