Theorem ltaddsub2d

Description: 'Less than' relationship between subtraction and addition. (Contributed by Mario Carneiro, 29-Dec-2016)

	Ref	Expression
Hypotheses	leidd.1	|- ( ph -> A e. RR )
	ltnegd.2	|- ( ph -> B e. RR )
	ltadd1d.3	|- ( ph -> C e. RR )
Assertion	ltaddsub2d	|- ( ph -> ( ( A + B ) < C <-> B < ( C - A ) ) )

Proof

Step	Hyp	Ref	Expression
1		leidd.1	|- ( ph -> A e. RR )
2		ltnegd.2	|- ( ph -> B e. RR )
3		ltadd1d.3	|- ( ph -> C e. RR )
4		ltaddsub2	|- ( ( A e. RR /\ B e. RR /\ C e. RR ) -> ( ( A + B ) < C <-> B < ( C - A ) ) )
5	1 2 3 4	syl3anc	|- ( ph -> ( ( A + B ) < C <-> B < ( C - A ) ) )