Metamath Proof Explorer


Theorem clnbgredg

Description: A vertices connected by an edge with another vertex is a neigborhood of those vertex. (Contributed by AV, 24-Aug-2025)

Ref Expression
Hypotheses clnbgredg.e 𝐸 = ( Edg ‘ 𝐺 )
clnbgredg.n 𝑁 = ( 𝐺 ClNeighbVtx 𝑋 )
Assertion clnbgredg ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝑌𝑁 )

Proof

Step Hyp Ref Expression
1 clnbgredg.e 𝐸 = ( Edg ‘ 𝐺 )
2 clnbgredg.n 𝑁 = ( 𝐺 ClNeighbVtx 𝑋 )
3 1 eleq2i ( 𝐾𝐸𝐾 ∈ ( Edg ‘ 𝐺 ) )
4 3 biimpi ( 𝐾𝐸𝐾 ∈ ( Edg ‘ 𝐺 ) )
5 4 3ad2ant1 ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → 𝐾 ∈ ( Edg ‘ 𝐺 ) )
6 simp3 ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → 𝑌𝐾 )
7 5 6 jca ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) )
8 7 anim2i ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ( 𝐺 ∈ UHGraph ∧ ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) ) )
9 3anass ( ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) ↔ ( 𝐺 ∈ UHGraph ∧ ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) ) )
10 8 9 sylibr ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) )
11 uhgredgrnv ( ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑌𝐾 ) → 𝑌 ∈ ( Vtx ‘ 𝐺 ) )
12 10 11 syl ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝑌 ∈ ( Vtx ‘ 𝐺 ) )
13 simp2 ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → 𝑋𝐾 )
14 5 13 jca ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) )
15 14 anim2i ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ( 𝐺 ∈ UHGraph ∧ ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) ) )
16 3anass ( ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) ↔ ( 𝐺 ∈ UHGraph ∧ ( 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) ) )
17 15 16 sylibr ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) )
18 uhgredgrnv ( ( 𝐺 ∈ UHGraph ∧ 𝐾 ∈ ( Edg ‘ 𝐺 ) ∧ 𝑋𝐾 ) → 𝑋 ∈ ( Vtx ‘ 𝐺 ) )
19 17 18 syl ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝑋 ∈ ( Vtx ‘ 𝐺 ) )
20 simpr1 ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝐾𝐸 )
21 sseq2 ( 𝑒 = 𝐾 → ( { 𝑋 , 𝑌 } ⊆ 𝑒 ↔ { 𝑋 , 𝑌 } ⊆ 𝐾 ) )
22 21 adantl ( ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) ∧ 𝑒 = 𝐾 ) → ( { 𝑋 , 𝑌 } ⊆ 𝑒 ↔ { 𝑋 , 𝑌 } ⊆ 𝐾 ) )
23 prssi ( ( 𝑋𝐾𝑌𝐾 ) → { 𝑋 , 𝑌 } ⊆ 𝐾 )
24 23 3adant1 ( ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) → { 𝑋 , 𝑌 } ⊆ 𝐾 )
25 24 adantl ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → { 𝑋 , 𝑌 } ⊆ 𝐾 )
26 20 22 25 rspcedvd ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ∃ 𝑒𝐸 { 𝑋 , 𝑌 } ⊆ 𝑒 )
27 26 olcd ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → ( 𝑌 = 𝑋 ∨ ∃ 𝑒𝐸 { 𝑋 , 𝑌 } ⊆ 𝑒 ) )
28 eqid ( Vtx ‘ 𝐺 ) = ( Vtx ‘ 𝐺 )
29 28 1 clnbgrel ( 𝑌 ∈ ( 𝐺 ClNeighbVtx 𝑋 ) ↔ ( ( 𝑌 ∈ ( Vtx ‘ 𝐺 ) ∧ 𝑋 ∈ ( Vtx ‘ 𝐺 ) ) ∧ ( 𝑌 = 𝑋 ∨ ∃ 𝑒𝐸 { 𝑋 , 𝑌 } ⊆ 𝑒 ) ) )
30 12 19 27 29 syl21anbrc ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝑌 ∈ ( 𝐺 ClNeighbVtx 𝑋 ) )
31 2 eleq2i ( 𝑌𝑁𝑌 ∈ ( 𝐺 ClNeighbVtx 𝑋 ) )
32 30 31 sylibr ( ( 𝐺 ∈ UHGraph ∧ ( 𝐾𝐸𝑋𝐾𝑌𝐾 ) ) → 𝑌𝑁 )