Theorem btwncolinear1

Description: Betweenness implies colinearity. (Contributed by Scott Fenton, 7-Oct-2013)

	Ref	Expression
Assertion	btwncolinear1	⊢ ( ( 𝑁 ∈ ℕ ∧ ( 𝐴 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐵 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐶 ∈ ( 𝔼 ‘ 𝑁 ) ) ) → ( 𝐶 Btwn ⟨ 𝐴 , 𝐵 ⟩ → 𝐴 Colinear ⟨ 𝐵 , 𝐶 ⟩ ) )

Proof

Step	Hyp	Ref	Expression
1		3mix3	⊢ ( 𝐶 Btwn ⟨ 𝐴 , 𝐵 ⟩ → ( 𝐴 Btwn ⟨ 𝐵 , 𝐶 ⟩ ∨ 𝐵 Btwn ⟨ 𝐶 , 𝐴 ⟩ ∨ 𝐶 Btwn ⟨ 𝐴 , 𝐵 ⟩ ) )
2		brcolinear	⊢ ( ( 𝑁 ∈ ℕ ∧ ( 𝐴 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐵 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐶 ∈ ( 𝔼 ‘ 𝑁 ) ) ) → ( 𝐴 Colinear ⟨ 𝐵 , 𝐶 ⟩ ↔ ( 𝐴 Btwn ⟨ 𝐵 , 𝐶 ⟩ ∨ 𝐵 Btwn ⟨ 𝐶 , 𝐴 ⟩ ∨ 𝐶 Btwn ⟨ 𝐴 , 𝐵 ⟩ ) ) )
3	1 2	imbitrrid	⊢ ( ( 𝑁 ∈ ℕ ∧ ( 𝐴 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐵 ∈ ( 𝔼 ‘ 𝑁 ) ∧ 𝐶 ∈ ( 𝔼 ‘ 𝑁 ) ) ) → ( 𝐶 Btwn ⟨ 𝐴 , 𝐵 ⟩ → 𝐴 Colinear ⟨ 𝐵 , 𝐶 ⟩ ) )