The set {0, 2, 5} is under addition, as is illustrated by the fact that adding 2 and 5 results in 7, which is not included in the set. The set of all integers is closed under addition, as is illustrated by the fact that adding -20 and 6 result in -14, which is in the set. The set of all polynomials is under addition, which is illustrated by the fact that adding 3x2 − 2 and 7x4 + 4x results in 7x4 + 3x2 + 4x − 2, which is in the set.