Theorem 7onn

Description: The ordinal 7 is a natural number. (Contributed by BTernaryTau, 4-Sep-2026)

	Ref	Expression
Assertion	7onn	⊢ 7o ∈ ω

Proof

Step	Hyp	Ref	Expression
1		df-7o	⊢ 7o = suc 6o
2		6onn	⊢ 6o ∈ ω
3		peano2	⊢ ( 6o ∈ ω → suc 6o ∈ ω )
4	2 3	ax-mp	⊢ suc 6o ∈ ω
5	1 4	eqeltri	⊢ 7o ∈ ω