move .is_separable() to child classes

sagemath · Jan 21, 2022 · a9b8ecc · a9b8ecc
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diff --git a/src/sage/schemes/elliptic_curves/ell_curve_isogeny.py b/src/sage/schemes/elliptic_curves/ell_curve_isogeny.py
@@ -2795,6 +2795,30 @@ def kernel_polynomial(self):
         return self.__kernel_polynomial
 
 
+    def is_separable(self):
+        r"""
+        Determine whether or not this isogeny is separable.
+
+        Since :class:`EllipticCurveIsogeny` only implements
+        separable isogenies, this method always returns ``True``.
+
+        EXAMPLES::
+
+            sage: E = EllipticCurve(GF(17), [0,0,0,3,0])
+            sage: phi = EllipticCurveIsogeny(E,  E((0,0)))
+            sage: phi.is_separable()
+            True
+
+        ::
+
+            sage: E = EllipticCurve('11a1')
+            sage: phi = EllipticCurveIsogeny(E, E.torsion_points())
+            sage: phi.is_separable()
+            True
+        """
+        return True
+
+
     def set_pre_isomorphism(self, preWI):
         r"""
         Modify this isogeny by precomposing with a Weierstrass isomorphism.

diff --git a/src/sage/schemes/elliptic_curves/hom.py b/src/sage/schemes/elliptic_curves/hom.py
@@ -407,27 +407,22 @@ def is_separable(self):
         r"""
         Determine whether or not this morphism is separable.
 
-        .. NOTE::
-
-           This method currently always returns ``True`` as Sage does
-           not yet implement inseparable isogenies. This will probably
-           change in the future.
-
-        EXAMPLES::
+        Implemented by child classes. For examples, see:
 
-            sage: E = EllipticCurve(GF(17), [0,0,0,3,0])
-            sage: phi = EllipticCurveIsogeny(E,  E((0,0)))
-            sage: phi.is_separable()
-            True
+        - :meth:`EllipticCurveIsogeny.is_separable`
+        - :meth:`sage.schemes.elliptic_curves.weierstrass_morphism.WeierstrassIsomorphism.is_separable`
+        - :meth:`sage.schemes.elliptic_curves.hom_composite.EllipticCurveHom_composite.is_separable`
+        - :meth:`sage.schemes.elliptic_curves.hom_scalar.EllipticCurveHom_scalar.is_separable`
 
-        ::
+        TESTS::
 
-            sage: E = EllipticCurve('11a1')
-            sage: phi = EllipticCurveIsogeny(E, E.torsion_points())
-            sage: phi.is_separable()
-            True
+            sage: from sage.schemes.elliptic_curves.hom import EllipticCurveHom
+            sage: EllipticCurveHom.is_separable(None)
+            Traceback (most recent call last):
+            ...
+            NotImplementedError: ...
         """
-        return True
+        raise NotImplementedError('children must implement')
 
     def is_surjective(self):
         r"""

diff --git a/src/sage/schemes/elliptic_curves/weierstrass_morphism.py b/src/sage/schemes/elliptic_curves/weierstrass_morphism.py
@@ -799,6 +799,21 @@ def kernel_polynomial(self):
         """
         return self._poly_ring(1)
 
+    def is_separable(self):
+        r"""
+        Determine whether or not this isogeny is separable.
+
+        Since :class:`WeierstrassIsomorphism` only implements
+        isomorphisms, this method always returns ``True``.
+
+        EXAMPLES::
+
+            sage: E = EllipticCurve(GF(31337), [0,1])
+            sage: {f.is_separable() for f in E.automorphisms()}
+            {True}
+        """
+        return True
+
     def dual(self):
         """
         Return the dual isogeny of this isomorphism.