Closure of an operator on a set means that if you take any two elements of the set and apply the operator to them, the result is also in the set. The set of natural numbers is a subset of the set of real numbers just means that all natural numbers are also real numbers.Natural numbers are always closed under addition and multiplication. Closure property of natural numbers states that the addition and multiplication of two or more natural numbers always result in a natural number. Closure property is one of the main properties used in math. By definition, closure property means the set is closed. In number theory, the partition function p(n) represents the number of possible partitions of a non-negative integer n. Closure property is a mathematical principle describing the way in which functions may be expanded to include one or more new variables. A natural number is closed under addition and multiplication. Information presented on the departments website is a representation of the existing wildfire situation, based on the information readily available to CAL FIRE.