code: def refine_pi_cation_laro(self, all_picat, stacks):
          
          i_set = []
          for picat in all_picat:
              exclude = False
              for stack in stacks:
                  if whichrestype(stack.proteinring.atoms[0]) == 'HIS' and picat.ring.obj == stack.ligandring.obj:
                      exclude = True
              if not exclude:
                  i_set.append(picat)
          return i_set
docs: Just important for constellations with histidine involved. If the histidine ring is positioned in stacking
          position to an aromatic ring in the ligand, there is in most cases stacking and pi-cation interaction reported
          as histidine also carries a positive charge in the ring. For such cases, only report stacking.