In Exercises 17–27, let the universe be the set Z + . Z+. Let X = { 1 , 2 , 3 , 4 , 5 } X={1, 2, 3, 4, 5} and let Y be the set of positive, even integers. In set-builder notation, Y = { 2 n | n ∈ Z + } . Y={2n|n∈Z+}. In Exercises 18–27, give a mathematical notation for the set by listing the elements if the set is finite, by using set-builder notation if the set is infinite, or by using a predefined set such as ∅ . ∅. A = { 1 , 3 , 5 } , B = { n | n ∈ Z + and n 2 − 1 ≤ n }