Theorem 7lt9

Description: 7 is less than 9. (Contributed by Mario Carneiro, 9-Mar-2015)

	Ref	Expression
Assertion	7lt9	|- 7 < 9

Proof

Step	Hyp	Ref	Expression
1		7lt8	|- 7 < 8
2		8lt9	|- 8 < 9
3		7re	|- 7 e. RR
4		8re	|- 8 e. RR
5		9re	|- 9 e. RR
6	3 4 5	lttri	|- ( ( 7 < 8 /\ 8 < 9 ) -> 7 < 9 )
7	1 2 6	mp2an	|- 7 < 9