Theorem orduni

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

	Ref	Expression
Assertion	orduni	⊢ ( Ord 𝐴 → Ord ∪ 𝐴 )

Proof

Step	Hyp	Ref	Expression
1		ordsson	⊢ ( Ord 𝐴 → 𝐴 ⊆ On )
2		ssorduni	⊢ ( 𝐴 ⊆ On → Ord ∪ 𝐴 )
3	1 2	syl	⊢ ( Ord 𝐴 → Ord ∪ 𝐴 )