Theorem ltsubposd

Description: Subtracting a positive number from another number decreases it. (Contributed by Mario Carneiro, 27-May-2016)

	Ref	Expression
Hypotheses	leidd.1	⊢ ( 𝜑 → 𝐴 ∈ ℝ )
	ltnegd.2	⊢ ( 𝜑 → 𝐵 ∈ ℝ )
Assertion	ltsubposd	⊢ ( 𝜑 → ( 0 < 𝐴 ↔ ( 𝐵 − 𝐴 ) < 𝐵 ) )

Proof

Step	Hyp	Ref	Expression
1		leidd.1	⊢ ( 𝜑 → 𝐴 ∈ ℝ )
2		ltnegd.2	⊢ ( 𝜑 → 𝐵 ∈ ℝ )
3		ltsubpos	⊢ ( ( 𝐴 ∈ ℝ ∧ 𝐵 ∈ ℝ ) → ( 0 < 𝐴 ↔ ( 𝐵 − 𝐴 ) < 𝐵 ) )
4	1 2 3	syl2anc	⊢ ( 𝜑 → ( 0 < 𝐴 ↔ ( 𝐵 − 𝐴 ) < 𝐵 ) )