Theorem iswlkon

Description: Properties of a pair of functions to be a walk between two given vertices (in an undirected graph). (Contributed by Alexander van der Vekens, 2-Nov-2017) (Revised by AV, 31-Dec-2020) (Revised by AV, 22-Mar-2021)

	Ref	Expression
Hypothesis	wlkson.v	⊢ 𝑉 = ( Vtx ‘ 𝐺 )
Assertion	iswlkon	⊢ ( ( ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ) ∧ ( 𝐹 ∈ 𝑈 ∧ 𝑃 ∈ 𝑍 ) ) → ( 𝐹 ( 𝐴 ( WalksOn ‘ 𝐺 ) 𝐵 ) 𝑃 ↔ ( 𝐹 ( Walks ‘ 𝐺 ) 𝑃 ∧ ( 𝑃 ‘ 0 ) = 𝐴 ∧ ( 𝑃 ‘ ( ♯ ‘ 𝐹 ) ) = 𝐵 ) ) )

Proof

Step	Hyp	Ref	Expression
1		wlkson.v	⊢ 𝑉 = ( Vtx ‘ 𝐺 )
2	1	wlkson	⊢ ( ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ) → ( 𝐴 ( WalksOn ‘ 𝐺 ) 𝐵 ) = { ⟨ 𝑓 , 𝑝 ⟩ ∣ ( 𝑓 ( Walks ‘ 𝐺 ) 𝑝 ∧ ( 𝑝 ‘ 0 ) = 𝐴 ∧ ( 𝑝 ‘ ( ♯ ‘ 𝑓 ) ) = 𝐵 ) } )
3		fveq1	⊢ ( 𝑝 = 𝑃 → ( 𝑝 ‘ 0 ) = ( 𝑃 ‘ 0 ) )
4	3	adantl	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → ( 𝑝 ‘ 0 ) = ( 𝑃 ‘ 0 ) )
5	4	eqeq1d	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → ( ( 𝑝 ‘ 0 ) = 𝐴 ↔ ( 𝑃 ‘ 0 ) = 𝐴 ) )
6		simpr	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → 𝑝 = 𝑃 )
7		fveq2	⊢ ( 𝑓 = 𝐹 → ( ♯ ‘ 𝑓 ) = ( ♯ ‘ 𝐹 ) )
8	7	adantr	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → ( ♯ ‘ 𝑓 ) = ( ♯ ‘ 𝐹 ) )
9	6 8	fveq12d	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → ( 𝑝 ‘ ( ♯ ‘ 𝑓 ) ) = ( 𝑃 ‘ ( ♯ ‘ 𝐹 ) ) )
10	9	eqeq1d	⊢ ( ( 𝑓 = 𝐹 ∧ 𝑝 = 𝑃 ) → ( ( 𝑝 ‘ ( ♯ ‘ 𝑓 ) ) = 𝐵 ↔ ( 𝑃 ‘ ( ♯ ‘ 𝐹 ) ) = 𝐵 ) )
11	2 5 10	2rbropap	⊢ ( ( ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ) ∧ 𝐹 ∈ 𝑈 ∧ 𝑃 ∈ 𝑍 ) → ( 𝐹 ( 𝐴 ( WalksOn ‘ 𝐺 ) 𝐵 ) 𝑃 ↔ ( 𝐹 ( Walks ‘ 𝐺 ) 𝑃 ∧ ( 𝑃 ‘ 0 ) = 𝐴 ∧ ( 𝑃 ‘ ( ♯ ‘ 𝐹 ) ) = 𝐵 ) ) )
12	11	3expb	⊢ ( ( ( 𝐴 ∈ 𝑉 ∧ 𝐵 ∈ 𝑉 ) ∧ ( 𝐹 ∈ 𝑈 ∧ 𝑃 ∈ 𝑍 ) ) → ( 𝐹 ( 𝐴 ( WalksOn ‘ 𝐺 ) 𝐵 ) 𝑃 ↔ ( 𝐹 ( Walks ‘ 𝐺 ) 𝑃 ∧ ( 𝑃 ‘ 0 ) = 𝐴 ∧ ( 𝑃 ‘ ( ♯ ‘ 𝐹 ) ) = 𝐵 ) ) )