Theorem uni0OLD

Description: Obsolete version of uni0 as of 1-Feb-2026. (Contributed by NM, 16-Sep-1993) Remove use of ax-nul . (Revised by Eric Schmidt, 4-Apr-2007) (Proof modification is discouraged.) (New usage is discouraged.)

	Ref	Expression
Assertion	uni0OLD	⊢ ∪ ∅ = ∅

Proof

Step	Hyp	Ref	Expression
1		0ss	⊢ ∅ ⊆ { ∅ }
2		uni0b	⊢ ( ∪ ∅ = ∅ ↔ ∅ ⊆ { ∅ } )
3	1 2	mpbir	⊢ ∪ ∅ = ∅