Mathematical concept-let G be a nonempty set and * be its algebraic operation, if the following conditions are met: 1. The associative law holds, that is, any element in G exists (a * b) * c = a * (b * c); Two. There is an element E in G, which is called the left unit element of G, and it has e * a = a three for every element A in G. For every element A in G, there is an element A (- 1) in G, which is called the left inverse of A, so A (-1) * A = E;