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Metamath Proof Explorer

Theorem usgr2wspthons3

Description: A simple path of length 2 between two vertices represented as length 3 string corresponds to two adjacent edges in a simple graph. (Contributed by Alexander van der Vekens, 8-Mar-2018) (Revised by AV, 17-May-2021) (Proof shortened by AV, 16-Mar-2022) (Revised by Ender Ting, 29-Jan-2026)

Ref Expression
Hypotheses usgr2wspthon0.v ⊢ 𝑉 = ( Vtx ‘ 𝐺 )
usgr2wspthon0.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
Assertion usgr2wspthons3 ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ↔ ( 𝐴 ≠ 𝐶 ∧ { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) )

Proof

Step Hyp Ref Expression
1 usgr2wspthon0.v ⊢ 𝑉 = ( Vtx ‘ 𝐺 )
2 usgr2wspthon0.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
3 2nn ⊢ 2 ∈ ℕ
4 ne0i ⊢ ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ≠ ∅ )
5 wspthsnonn0vne ⊢ ( ( 2 ∈ ℕ ∧ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ≠ ∅ ) → 𝐴 ≠ 𝐶 )
6 3 4 5 sylancr ⊢ ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → 𝐴 ≠ 𝐶 )
7 simplr ⊢ ( ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ) → 𝐴 ≠ 𝐶 )
8 wpthswwlks2on ⊢ ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) → ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) = ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) )
9 8 eleq2d ⊢ ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ↔ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) )
10 9 biimpa ⊢ ( ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ) → ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) )
11 7 10 jca ⊢ ( ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ) → ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) )
12 11 exp31 ⊢ ( 𝐺 ∈ USGraph → ( 𝐴 ≠ 𝐶 → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) ) )
13 12 com13 ⊢ ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → ( 𝐴 ≠ 𝐶 → ( 𝐺 ∈ USGraph → ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) ) )
14 6 13 mpd ⊢ ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → ( 𝐺 ∈ USGraph → ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) )
15 14 com12 ⊢ ( 𝐺 ∈ USGraph → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) → ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) )
16 9 biimprd ⊢ ( ( 𝐺 ∈ USGraph ∧ 𝐴 ≠ 𝐶 ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) → ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ) )
17 16 expimpd ⊢ ( 𝐺 ∈ USGraph → ( ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) → ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ) )
18 15 17 impbid ⊢ ( 𝐺 ∈ USGraph → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ↔ ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) )
19 18 adantr ⊢ ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ↔ ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ) )
20 1 2 usgrwwlks2on ⊢ ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ↔ ( { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) )
21 20 anbi2d ⊢ ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ↔ ( 𝐴 ≠ 𝐶 ∧ ( { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) ) )
22 3anass ⊢ ( ( 𝐴 ≠ 𝐶 ∧ { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ↔ ( 𝐴 ≠ 𝐶 ∧ ( { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) )
23 21 22 bitr4di ⊢ ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ( 𝐴 ≠ 𝐶 ∧ ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WWalksNOn 𝐺 ) 𝐶 ) ) ↔ ( 𝐴 ≠ 𝐶 ∧ { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) )
24 19 23 bitrd ⊢ ( ( 𝐺 ∈ USGraph ∧ ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ∧ 𝐶 ∈ 𝑉 ) ) → ( ⟨“ 𝐴 𝐵 𝐶 ”⟩ ∈ ( 𝐴 ( 2 WSPathsNOn 𝐺 ) 𝐶 ) ↔ ( 𝐴 ≠ 𝐶 ∧ { 𝐴 , 𝐵 } ∈ 𝐸 ∧ { 𝐵 , 𝐶 } ∈ 𝐸 ) ) )