Theorem 4lt9

Description: 4 is less than 9. (Contributed by Mario Carneiro, 9-Mar-2015)

	Ref	Expression
Assertion	4lt9	$$⊢4<9$$

Proof

Step	Hyp	Ref	Expression
1		4lt5	$$⊢4<5$$
2		5lt9	$$⊢5<9$$
3		4re	$$⊢4\in ℝ$$
4		5re	$$⊢5\in ℝ$$
5		9re	$$⊢9\in ℝ$$
6	3 4 5	lttri	$$⊢\left(4<5\wedge 5<9\right)\to 4<9$$
7	1 2 6	mp2an	$$⊢4<9$$