Definition 1. Let $a$ and $b$ be two sets. The pair of $a$ and $b$ is
\[\{a, b\} = \{x : x = a \lor x = b\}.\]This is a set by Axiom of Pairing.
Proposition 2 (Unorderedness). For any sets $a$ and $b$,
\[\{a, b\} = \{b, a\}.\]Pub Feb 16, 2026 Up Aug 03, 2026
Definition 1. Let $a$ and $b$ be two sets. The pair of $a$ and $b$ is
\[\{a, b\} = \{x : x = a \lor x = b\}.\]This is a set by Axiom of Pairing.
Proposition 2 (Unorderedness). For any sets $a$ and $b$,
\[\{a, b\} = \{b, a\}.\]