S={，，}

Extended data r.s = {<1,3 >; ，& lt2，4 >，& lt 1， 1 & gt； ,<3 > Synthesis of binary relations r and s (also called synthesis). R*S is a set of ordered pairs, and a set cannot have duplicate elements. No matter how many elements are repeated, only one can be retained.

Discrete mathematics is a mathematical discipline that studies the structure and relationship of discrete quantities and an important branch of modern mathematics. The meaning of discreteness refers to different connecting elements, and the structure based on discreteness and the relationship between them are mainly studied. The objects are generally finite or countable elements. Discrete mathematics is widely used in various disciplines, especially in the field of computer science and technology. At the same time, discrete mathematics is also a specialized course for computer majors, such as programming language, data structure, operating system, compilation technology, artificial intelligence, database, algorithm design and analysis, theoretical computer science foundation and so on. Through the study of discrete mathematics, we can not only master the descriptive tools and methods for dealing with discrete structures, but also create conditions for subsequent courses, improve abstract thinking and strict logical reasoning ability, and lay a solid foundation for participating in innovative research and development in the future.