def __eq__(self,other):
        '''
        x == y iff x and y have:
                 1. an equal number of vertices
                 2. the same vertices
        '''

        return len(set(self.vertices).difference(set(other.vertices))) == 0
def __eq__ ( self , other ) : return len ( set ( self . vertices ) . difference ( set ( other . vertices ) ) ) == 0
x == y iff x and y have:
                 1. an equal number of vertices
                 2. the same vertices