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Metamath Proof Explorer

Theorem hashwwlksnext

Description: Number of walks (as words) extended by an edge as a sum over the prefixes. (Contributed by Alexander van der Vekens, 21-Aug-2018) (Revised by AV, 20-Apr-2021) (Revised by AV, 26-Oct-2022)

Ref Expression
Hypotheses wwlksnextprop.x ⊢ 𝑋 = ( ( 𝑁 + 1 ) WWalksN 𝐺 )
wwlksnextprop.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
wwlksnextprop.y ⊢ 𝑌 = { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 }
Assertion hashwwlksnext ( ( Vtx ‘ 𝐺 ) ∈ Fin → ( ♯ ‘ { 𝑥 ∈ 𝑋 ∣ ∃ 𝑦 ∈ 𝑌 ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ) = Σ 𝑦 ∈ 𝑌 ( ♯ ‘ { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ) )

Proof

Step Hyp Ref Expression
1 wwlksnextprop.x ⊢ 𝑋 = ( ( 𝑁 + 1 ) WWalksN 𝐺 )
2 wwlksnextprop.e ⊢ 𝐸 = ( Edg ‘ 𝐺 )
3 wwlksnextprop.y ⊢ 𝑌 = { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 }
4 wwlksnfi ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → ( 𝑁 WWalksN 𝐺 ) ∈ Fin )
5 ssrab2 ⊢ { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 } ⊆ ( 𝑁 WWalksN 𝐺 )
6 ssfi ⊢ ( ( ( 𝑁 WWalksN 𝐺 ) ∈ Fin ∧ { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 } ⊆ ( 𝑁 WWalksN 𝐺 ) ) → { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 } ∈ Fin )
7 4 5 6 sylancl ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → { 𝑤 ∈ ( 𝑁 WWalksN 𝐺 ) ∣ ( 𝑤 ‘ 0 ) = 𝑃 } ∈ Fin )
8 3 7 eqeltrid ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → 𝑌 ∈ Fin )
9 wwlksnfi ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → ( ( 𝑁 + 1 ) WWalksN 𝐺 ) ∈ Fin )
10 1 9 eqeltrid ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → 𝑋 ∈ Fin )
11 rabfi ⊢ ( 𝑋 ∈ Fin → { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ∈ Fin )
12 10 11 syl ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ∈ Fin )
13 12 adantr ⊢ ( ( ( Vtx ‘ 𝐺 ) ∈ Fin ∧ 𝑦 ∈ 𝑌 ) → { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ∈ Fin )
14 1 2 3 disjxwwlkn ⊢ Disj 𝑦 ∈ 𝑌 { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) }
15 14 a1i ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → Disj 𝑦 ∈ 𝑌 { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } )
16 8 13 15 hashrabrex ⊢ ( ( Vtx ‘ 𝐺 ) ∈ Fin → ( ♯ ‘ { 𝑥 ∈ 𝑋 ∣ ∃ 𝑦 ∈ 𝑌 ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ) = Σ 𝑦 ∈ 𝑌 ( ♯ ‘ { 𝑥 ∈ 𝑋 ∣ ( ( 𝑥 prefix 𝑀 ) = 𝑦 ∧ ( 𝑦 ‘ 0 ) = 𝑃 ∧ { ( lastS ‘ 𝑦 ) , ( lastS ‘ 𝑥 ) } ∈ 𝐸 ) } ) )