Theorem orduniss 6456

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

Assertion

Ref	Expression
orduniss	⊢ (Ord 𝐴 → ∪ 𝐴 ⊆ 𝐴)

Proof of Theorem orduniss

Step	Hyp	Ref	Expression
1		ordtr 6371	. 2 ⊢ (Ord 𝐴 → Tr 𝐴)
2		df-tr 5235	. 2 ⊢ (Tr 𝐴 ↔ ∪ 𝐴 ⊆ 𝐴)
3	1, 2	sylib 218	1 ⊢ (Ord 𝐴 → ∪ 𝐴 ⊆ 𝐴)

Syntax hints:   → wi 4   ⊆ wss 3931  ∪ cuni 4888  Tr wtr 5234  Ord word 6356

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 207  df-an 396  df-tr 5235  df-ord 6360

This theorem is referenced by:  orduniorsuc  7829  onfununi  8360  rankuniss  9885  r1limwun  10755  ontgval  36454  onsupneqmaxlim0  43215  onsupnmax  43219