ABSTRACT
This appendix briefly introduces basic notations and notions of set theory used in this book.
The notion of a set as a mathematical term was introduced by Georg Cantor in 1877 who defined a set as “a collection of certain well-distinguished objects of cognition or thinking, which will be called elements, to a whole.” Conventionally sets are represented by capital letters whereas lowercase
letters are used to denote their elements. In order to express that an entity e is an element of a set S, we write e ∈ S (the contrary would be displayed as e 6∈ S). Note that a set cannot contain an element twice or many times, rather, the
element is either contained or not.
