Science:Math Exam Resources/Courses/MATH220/December 2011/Question 01 (b)/Solution 1
The set X is the intersection of all of the sets Sα; that is, X is the set of all x such that, for all α ∈ I we have x ∈ Sα.
The set Y is the union of all of the sets Sα; that is, Y is the set of all y such that there exists an α ∈ I such that y ∈ Sα.