Concepts used extensively in the subsequent chapters of the book are reviewed and illustrated by simple examples. The review includes linear, normed, Hilbert, and metric spaces, topology induced on metric spaces by their metrics, \(\sigma \) -fields on metric spaces, the space of real-valued continuous functions C[0, \(\tau \) ] defined on bounded time intervals [0, \(\tau \) ], random processes with continuous paths, convergence in C[0, \(\tau \) ], and continuous mapping theorem, an essential tool for characterizing extremes of target processes by those of their FD models.