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I was just brushing up on my discrete mathematics specifically graph theory and read the following definition of a walk in a graph

"A walk in a graph is an alternating sequence of vertices and edges from a start vertex to an end vertex where start and the end vertices are not necessarily distinct"

and after this I read up the definition of a path in a graph which says

"A path in a graph is a walk in the graph with no repeated vertices"

the point of confusion is that the definition for a path doesn't mention anything about the repetition of edges in a path, although the idea of repetition of edge in a path sounds absurd to me because that eventually means that I am taking the same road that I traversed previously and hence repeating the same destinations which are the vertices respectively. I am curious to know if there is any such case of a path where there is a repetitive edge but no repeated vertex.

One more thing I would like to know is can there exists an ordering of edges in a graph such that the path from one vertex to another is infinite in short can there be an infinite path in a finite graph?

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up vote 2 down vote accepted

The terminology varies a bit from textbook to textbook, so it's always a good idea to check the conventions used by that particular author.

I assume that the definitions you work with are the ones you state. Then there can not be a repeated edge in a path. If an edge occurs twice in the same path, then both of its endpoints would also occur twice among the visited vertices.

For the second question, a finite graph has a finite number of edges and a finite number of vertices, so as long as no repetition are allowed, a path would have to be finitely long.

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The thing is a walk can have repeated vertices and edges but a path is a special type of walk where no vertex is repeated – AnkitSablok Jun 10 '13 at 13:02

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