Theorem 9m1e8

Description: 9 - 1 = 8. (Contributed by AV, 6-Sep-2021)

	Ref	Expression
Assertion	9m1e8	$$⊢9-1=8$$

Proof

Step	Hyp	Ref	Expression
1		8cn	$$⊢8\in ℂ$$
2		ax-1cn	$$⊢1\in ℂ$$
3		df-9	$$⊢9=8+1$$
4	1 2 3	mvrraddi	$$⊢9-1=8$$