In my definition, this is a closed walk? If yes, how can I enumerate the vertices? In this picture, who is $v_1, v_2,...$?

Definition: A closed walk in a graph is defined to be ordered collection of vertices $(v_1,v_2,...,v_n)$ such that $v_i$ and $v_{i+1}$ are neighbours for all $1 \leq i \leq n-1$, and $v_n$ and $v_1$ are neighbours. Note that the walk is allowed to visit the same vertex or traverse the same edge on more than one occasion.enter image description here

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    $\begingroup$ No, the picture is not a closed walk, because a closed walk is a sequence of vertices, and the picture is not a sequence of vertices. $\endgroup$ – Misha Lavrov Dec 13 '18 at 21:45
  • $\begingroup$ @MishaLavrov could you give me an example of closed walk that we have at least two visits the same vertex and/or at least two traverse the same edge? I can't imagine an example. Thanks $\endgroup$ – Pedro Salgado Dec 13 '18 at 21:49
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    $\begingroup$ Get a "triangle" graph with vertices $v_1,\, v_2,\, v_3$. $(v_1,\, v_2,\, v_3, \,v_1,\, v_2,\, v_3)$ is one of such closed walks. $\endgroup$ – Lucas Henrique Dec 13 '18 at 22:00

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