sage: p = 1019
sage: F = GF(p)
sage: E = EllipticCurve(F,[1,-1,0,1,1])
sage: psi = E.division_polynomial(7).factor()[3][0]
sage: phi = E.isogeny(kernel=psi)
sage: assert phi.degree()==7
sage: phi.dual()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)

/home/jec/.sage/temp/selmer/14232/_home_jec__sage_init_sage_0.py in <module>()

/home/jec/sage-4.1.2.rc0/local/lib/python2.6/site-packages/sage/schemes/elliptic_curves/ell_curve_isogeny.pyc in dual(self)
   2998
   2999         phi_hat.set_pre_isomorphism(pre_isom)
-> 3000         phi_hat.set_post_isomorphism(post_isom)
   3001
   3002         self.__dual = phi_hat

/home/jec/sage-4.1.2.rc0/local/lib/python2.6/site-packages/sage/schemes/elliptic_curves/ell_curve_isogeny.pyc in set_post_isomorphism(self, postWI)
   2627
   2628         if (self.__E2 != WIdom):
-> 2629             raise ValueError, "Invalid parameter: isomorphism must have domain curve equal to this isogenies'codomain."
   2630
   2631         if (None == self.__post_isomorphism):

ValueError: Invalid parameter: isomorphism must have domain curve equal to this isogenies' codomain.