This is an inofficial mirror of http://metamath.tirix.org for personal testing of a visualizer extension only.

Metamath Proof Explorer

Theorem orduni

Description: The union of an ordinal class is ordinal. (Contributed by NM, 12-Sep-2003)

		Ref	Expression
	Assertion	orduni	$⊢ Ord A \to Ord ⋃ A$

Step	Hyp	Ref	Expression
1		ordsson	$⊢ Ord A \to A \subseteq On$
2		ssorduni	$⊢ A \subseteq On \to Ord ⋃ A$
3	1 2	syl	$⊢ Ord A \to Ord ⋃ A$