Triangular norms by Erich Peter Klement, Radko Mesiar, and Endre Pap

Background: Why t-norms? Until the early 1960s, uncertainty had been described by probability theory. In probability theory, our uncertainty in a statement A is described by its probability p(A), which is a number from the interval [0, 1]. After that, several other formalisms have appeared that describe degrees of uncertainty, vagueness, and so on. Most of these formalisms also use values from the interval [0, 1] to describe the corresponding degrees. In each of these formalisms, we encounter a similar problem: