[W/K] :: depth-first search

  depth-first search
       
           A graph search algorithm which extends the
          current path as far as possible before backtracking to the
          last choice point and trying the next alternative path.
          Depth-first search may fail to find a solution if it enters a
          cycle in the graph.  This can be avoided if we never extend a
          path to a node which it already contains.
       
          Opposite of breadth first search.  See also iterative
          deepening.
       
          (1995-04-19)