def delete_edge(nodeidentifier, *edges)
      alledges = @edges[nodeidentifier]
      edges.each { |edge| alledges.delete edge }
    end
def delete_edge(nodeidentifier, *edges)
      alledges = @edges[nodeidentifier]
      edges.each { |edge| alledges.delete edge }
    end
Removal - deletes the edge(s) +:edges+ connected to the node
 referenced by +:nodeidentifer+.