Theorem tsetndxnn

Description: The index of the slot for the group operation in an extensible structure is a positive integer. (Contributed by AV, 31-Oct-2024)

	Ref	Expression
Assertion	tsetndxnn	⊢ ( TopSet ‘ ndx ) ∈ ℕ

Proof

Step	Hyp	Ref	Expression
1		tsetndx	⊢ ( TopSet ‘ ndx ) = 9
2		9nn	⊢ 9 ∈ ℕ
3	1 2	eqeltri	⊢ ( TopSet ‘ ndx ) ∈ ℕ