For example:

R = { & lt 1，2 & gt； ，& lt2，3 >，& lt 1，4 & gt； ，& lt3， 1 & gt； }

S = { & lt2，3 >，& lt3，4 >，& lt 1，2 & gt； ，& lt4， 1 & gt； }

r .S = { & lt 1，3 & gt； ，& lt2，4 >，& lt 1， 1 & gt； ，& lt3，2 >}

s .R = { & lt2， 1 & gt； ，& lt 1，3 & gt； ，& lt4，2 >，& lt4，4 >}

Discrete mathematics is traditional logic.

Set theory (including function), number theory foundation, algorithm design, combinatorial analysis, discrete probability, relation theory, graph theory and tree, abstract algebra (including algebraic system, group, ring, field, etc. ), Boolean algebra, computational models (languages and automata) and so on. The application of discrete mathematics covers many fields of modern science and technology.