. vertex   tree   --   visited

                   fringe  --  adjacent to tree vertices, but not visited yet

                   unseen  --  not encountered  ( priority = unseen = "infinite" )

    . Algorithm

         .  remove vertex  x  from fringe (  priority queue  )

         .  put unseen vertices adjacent to  x  on fringe

 
    . Depth - First search
  
   . Breadth - First search