Inverted A is a symbol in discrete mathematics. Inverted a means arbitrary, arbitrary. Full name quantifier (arbitrary quantifier). Discrete mathematics is a mathematical discipline that studies the structure and relationship of discrete quantities and an important branch of modern mathematics.

The subject content of discrete mathematics is 1. Set theory: set and its operation, binary relation and function, natural number and natural number set, cardinality of set.

2. Graph theory: basic concepts of graphs, Euler graphs and hamiltonian graph, matrix representation of trees and graphs, planar graphs, graph coloring, dominating sets, covering sets, independent sets and matching, weighted graphs and their applications.

3. Algebraic structure: the basic concepts of algebraic system, semigroup and singularity, group, ring and field, lattice and Boolean algebra.

4. Combinatorial mathematics: combinatorial existence theorem, basic counting formula, combinatorial counting method and combinatorial counting theorem.

5. Mathematical logic: propositional logic, first-order predicate calculus and resolution principle.