Find the complement of b first, and then find the intersection with a, and the combination of numbers in the intersection is a subset.

C is the symbol of complement set, R is the set of real numbers, representing all real numbers, CRB is the complement set of finding b ∩ is the symbol of intersection, which is the intersection of A and B, and the combination of intersection numbers is the subset.

Subset is a mathematical concept: if any element of set A is an element of set B, then set A is called a subset of set B. Symbolic language: if _a∈A has a∈B, then a _ B. If any element of set A is an element of set B (any A is a∈B), then set A is called set B.