code: def is_periodically_contiguous( self ):
          
          edges = self.sites_at_edges()
          is_contiguous = [ False, False, False ]
          along_x = any( [ s2 in s1.p_neighbours for s1 in edges[0] for s2 in edges[1] ] )
          along_y = any( [ s2 in s1.p_neighbours for s1 in edges[2] for s2 in edges[3] ] )
          along_z = any( [ s2 in s1.p_neighbours for s1 in edges[4] for s2 in edges[5] ] )
          return ( along_x, along_y, along_z )
docs: logical check whether a cluster connects with itself across the
          simulation periodic boundary conditions.
  
          Args:
              none
  
          Returns
              ( Bool, Bool, Bool ): Contiguity along the x, y, and z coordinate axes