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Database GRAPH THEORY Undirected graphs Neighbors, complete graphs and universal vertices Neighbors nbusgr
Description: The set of neighbors of an arbitrary class in a simple graph.
(Contributed by Alexander van der Vekens , 9-Oct-2017) (Revised by AV , 26-Oct-2020) (Proof shortened by AV , 27-Nov-2020)
Ref
Expression
Hypotheses
nbuhgr.v ⊢ 𝑉 = ( Vtx ‘ 𝐺 )
nbuhgr.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
Assertion
nbusgr ⊢ ( 𝐺 ∈ USGraph → ( 𝐺 NeighbVtx 𝑁 ) = { 𝑛 ∈ 𝑉 ∣ { 𝑁 , 𝑛 } ∈ 𝐸 } )
Proof
Step
Hyp
Ref
Expression
1
nbuhgr.v ⊢ 𝑉 = ( Vtx ‘ 𝐺 )
2
nbuhgr.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
3
usgrumgr ⊢ ( 𝐺 ∈ USGraph → 𝐺 ∈ UMGraph )
4
1 2
nbumgr ⊢ ( 𝐺 ∈ UMGraph → ( 𝐺 NeighbVtx 𝑁 ) = { 𝑛 ∈ 𝑉 ∣ { 𝑁 , 𝑛 } ∈ 𝐸 } )
5
3 4
syl ⊢ ( 𝐺 ∈ USGraph → ( 𝐺 NeighbVtx 𝑁 ) = { 𝑛 ∈ 𝑉 ∣ { 𝑁 , 𝑛 } ∈ 𝐸 } )