Jacques Neveu, Mathematical Foundations of the Calculus of Probability, Holden-Day, San Francisco. Random variables and the associated probability theory and conditional probability theory are surprisingly relevant, especially now with computing, in the real world. That the set of real valued random variables X such that E[X^2] is finite forms a Hilbert space, e.g., is complete, is astounding. So is the martingale convergence theorem. Erich Fromm, The Art of Loving. Heavily about how what people do is in response to the anxiety they feel from the realization that alone they are vulnerable to the hostile forces of nature and society.
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