\(X\cup Y = \{t\mid t \in X \vee t \in Y\}\) (\(\vee\) means "or") intersection : \(X\cap Y = \{t\mid t\in X \wedge t\in Y\}\) complement : \(\complement X = \{t \mid t \notin X\}\) (unordered) pair : \(\{t,u\} = \{t\}\cup\{u\}\) ordered pair : \((t,u) = \{t, \{t, u\}\}\) power set