src/sage/rings/polynomial/multi_polynomial_libsingular.pyx: Replace pbori import

Author: Matthias Koeppe

src/sage/rings/polynomial/multi_polynomial_libsingular.pyx

@@ -213,6 +213,7 @@ from sage.libs.singular.ring cimport singular_ring_new, singular_ring_reference,
 
 # polynomial imports
 from sage.rings.polynomial.multi_polynomial_ring import MPolynomialRing_polydict, MPolynomialRing_polydict_domain
+from sage.rings.polynomial.multi_polynomial_ring_base import BooleanPolynomialRing_base
 from sage.rings.polynomial.multi_polynomial_element import MPolynomial_polydict
 from sage.rings.polynomial.multi_polynomial_ideal import MPolynomialIdeal
 from sage.rings.polynomial.polydict cimport ETuple
@@ -948,8 +949,7 @@ cdef class MPolynomialRing_libsingular(MPolynomialRing_base):
                     raise
             return new_MP(self, _p)
 
-        from sage.rings.polynomial.pbori.pbori import BooleanPolynomial
-        if isinstance(element, BooleanPolynomial):
+        if isinstance(element, Element) and isinstance(element.parent(), BooleanPolynomialRing_base):
             if element.constant():
                 if element:
                     return self._one_element