Theorem orduniss

Description: An ordinal class includes its union. (Contributed by NM, 13-Sep-2003)

	Ref	Expression
Assertion	orduniss	$$⊢\mathrm{Ord}A\to \bigcup A\subseteq A$$

Proof

Step	Hyp	Ref	Expression
1		ordtr	$$⊢\mathrm{Ord}A\to \mathrm{Tr}A$$
2		df-tr	$$⊢\mathrm{Tr}A\leftrightarrow \bigcup A\subseteq A$$
3	1 2	sylib	$$⊢\mathrm{Ord}A\to \bigcup A\subseteq A$$