Theorem ltsub1dd

Description: Subtraction from both sides of 'less than'. (Contributed by Mario Carneiro, 30-May-2016)

	Ref	Expression
Hypotheses	leidd.1	$$⊢\phi \to A\in ℝ$$
	ltnegd.2	$$⊢\phi \to B\in ℝ$$
	ltadd1d.3	$$⊢\phi \to C\in ℝ$$
	ltadd1dd.4	$$⊢\phi \to A<B$$
Assertion	ltsub1dd	$$⊢\phi \to A-C<B-C$$

Proof

Step	Hyp	Ref	Expression
1		leidd.1	$$⊢\phi \to A\in ℝ$$
2		ltnegd.2	$$⊢\phi \to B\in ℝ$$
3		ltadd1d.3	$$⊢\phi \to C\in ℝ$$
4		ltadd1dd.4	$$⊢\phi \to A<B$$
5	1 2 3	ltsub1d	$$⊢\phi \to \left(A<B\leftrightarrow A-C<B-C\right)$$
6	4 5	mpbid	$$⊢\phi \to A-C<B-C$$