[K] is a group of natural numbers, and its remainder divided by 4 is K, so the meaning of [K]+[M] should be to add a number to each of these two groups of numbers and divide by 4 to see which remainder is 0 ~ 3. For example, [1]+[3] means that the remainder is 1+3=4, which is a multiple of 4, so the sum is [0].

Discrete mathematics

It is a comprehensive subject that integrates traditional logic, set theory (including functions), number theory foundation, algorithm design, combinatorial analysis, discrete probability, relational theory, graph theory and tree, and 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.