Theorem ltsub23d

Description: 'Less than' relationship between subtraction and addition. (Contributed by Mario Carneiro, 27-May-2016)

	Ref	Expression
Hypotheses	leidd.1	⊢ ( 𝜑 → 𝐴 ∈ ℝ )
	ltnegd.2	⊢ ( 𝜑 → 𝐵 ∈ ℝ )
	ltadd1d.3	⊢ ( 𝜑 → 𝐶 ∈ ℝ )
	ltsub23d.4	⊢ ( 𝜑 → ( 𝐴 − 𝐵 ) < 𝐶 )
Assertion	ltsub23d	⊢ ( 𝜑 → ( 𝐴 − 𝐶 ) < 𝐵 )

Proof

Step	Hyp	Ref	Expression
1		leidd.1	⊢ ( 𝜑 → 𝐴 ∈ ℝ )
2		ltnegd.2	⊢ ( 𝜑 → 𝐵 ∈ ℝ )
3		ltadd1d.3	⊢ ( 𝜑 → 𝐶 ∈ ℝ )
4		ltsub23d.4	⊢ ( 𝜑 → ( 𝐴 − 𝐵 ) < 𝐶 )
5		ltsub23	⊢ ( ( 𝐴 ∈ ℝ ∧ 𝐵 ∈ ℝ ∧ 𝐶 ∈ ℝ ) → ( ( 𝐴 − 𝐵 ) < 𝐶 ↔ ( 𝐴 − 𝐶 ) < 𝐵 ) )
6	1 2 3 5	syl3anc	⊢ ( 𝜑 → ( ( 𝐴 − 𝐵 ) < 𝐶 ↔ ( 𝐴 − 𝐶 ) < 𝐵 ) )
7	4 6	mpbid	⊢ ( 𝜑 → ( 𝐴 − 𝐶 ) < 𝐵 )