revise a notation

rw.org

@@ -53,7 +53,7 @@ graph rather than the directed graph for its simplicity.
 Random walk on a graph is a series of movements that an /agent/, i.e.,
 walker, traverses a graph.  Specifically, the operation of an agent is
 described as follows; (i) an agent on vertex $u$ randomly selects
-vertex $v$ of vertices that are adjacent to vertex $v$, and the agent
+vertex $v$ of vertices that are adjacent to vertex $u$, and the agent
 moves to the randomly-selected vertex $v$ among adjacent vertices;
 (ii) procedure (i) is repeated until a given condition is satisfied.
 Strictly speaking, at step $t$, an agent on vertex $u$ selects vertex