@staticmethod
def conv_equa(list_surface):
    """Method converting a list of if of surface and return a tuple with
        the informations of the volume EQUA T4"""
    minus_surfs = []
    plus_surfs = []
    seen = set()
    for elt in list_surface:
        assert isinstance(elt, int)
        if elt in seen:
            continue
        seen.add(elt)
        if elt < 0:
            minus_surfs.append(-elt)
        elif elt > 0:
            plus_surfs.append(elt)
    return plus_surfs, minus_surfs
