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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def refine_pi_cation_laro(self, all_picat, stacks):
 """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. """

        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