def ltrim(f, gen):
        """
        Remove dummy generators from the "left" of ``f``.

        Examples
        ========

        >>> from sympy import Poly
        >>> from sympy.abc import x, y, z

        >>> Poly(y**2 + y*z**2, x, y, z).ltrim(y)
        Poly(y**2 + y*z**2, y, z, domain='ZZ')

        """
        rep = f.as_dict(native=True)
        j = f._gen_to_level(gen)
        terms = {}

        for monom, coeff in rep.items():
            monom = monom[j:]

            if monom not in terms:
                terms[monom] = coeff
            else:
                raise PolynomialError("can't left trim %s" % f)

        gens = f.gens[j:]

        return f.new(DMP.from_dict(terms, len(gens) - 1, f.rep.dom), *gens)
dataset/ETHPy150Open sympy/sympy/sympy/polys/polytools.py/Poly.ltrim/original