The number formula of set proper subset is 2 n- 1. For a set with n elements, its * * * has 2 n subsets, and the number of proper subset is minus 1. If any element of set A is an element of set B, then set A is called a subset of set B. ..

Sets are divided into empty sets and non-empty sets:

1. If it is an empty set, only one subset is itself, and there is no proper subset.

2. If it is a non-empty set, if there are n elements in a set, the number of subsets of this set is 2 n, and the number of proper subset is (2 n)- 1.

In mathematics, physics, chemistry, biology and other natural sciences, mathematical symbols are used to express the relationship between several quantities. It is universal and applicable to all similar problems. In mathematical logic, a formula is a formal grammatical object to express a proposition, but the proposition may depend on the free variable value of the formula.

The precise definition of a formula depends on the specific formal logic involved, but there is a very typical definition (for first-order logic): the formula is defined relative to a specific language; That is, a set of constant symbols, function symbols and relational symbols, in which each function and relational symbol has an arity to indicate the number of parameters it accepts.