def METHOD_NAME(self):
    """Fateman's GCD benchmark: sparse inputs (deg f ~ vars f)."""
    gens = self.gens
    x = gens[0]
    n = self.ngens
    D = (1 + sum(_**n for _ in gens))**2
    return (D*(-2 + x**n - sum(_**n for _ in gens[1:]))**2,
            D*(+2 + sum(_**n for _ in gens))**2, D)