def find_connection(v1, v2)
      raise "not a vertex" unless v1.is_a?(Vertex) && v2.is_a?(Vertex)
      raise "Vertices not connected" if !is_connected?(v1, v2)
      connection = v1.edges.select {|edge| edge.connection.include?(v2)}
      raise "Error finding connection" if connection.length > 1
      connection.first
    end
def find_connection(v1, v2)
      raise "not a vertex" unless v1.is_a?(Vertex) && v2.is_a?(Vertex)
      raise "Vertices not connected" if !is_connected?(v1, v2)
      connection = v1.edges.select {|edge| edge.connection.include?(v2)}
      raise "Error finding connection" if connection.length > 1
      connection.first
    end
Find the edge connecting two vertices