Having is_submodule not error out for different ambient spaces.

Author: tscrim

src/sage/combinat/specht_module.py

@@ -84,7 +84,6 @@ def frobenius_image(self):
 
         EXAMPLES::
 
-            sage: s = SymmetricFunctions(QQ).s()
             sage: SM = Partition([2,2,1]).specht_module(QQ)
             sage: SM.frobenius_image()
             s[2, 2, 1]
@@ -99,6 +98,7 @@ def frobenius_image(self):
             sage: F = D.specht_module(QQ).frobenius_image(); F
             s[1, 1, 1, 1, 1] + 4*s[2, 1, 1, 1] + 5*s[2, 2, 1]
              + 6*s[3, 1, 1] + 5*s[3, 2] + 4*s[4, 1] + s[5]
+            sage: s = SymmetricFunctions(QQ).s()
             sage: F == sum(StandardTableaux(la).cardinality() * s[la]
             ....:          for la in Partitions(5))
             True

src/sage/modules/with_basis/subquotient.py

@@ -394,21 +394,19 @@ def is_submodule(self, other):
             sage: H.is_submodule(G)
             False
 
-        TESTS::
+        Different ambient spaces::
 
             sage: X = CombinatorialFreeModule(QQ, range(4)); x = X.basis()
             sage: F = X.submodule([x[0]-x[1], x[1]-x[2], x[2]-x[3]])
             sage: Y = CombinatorialFreeModule(QQ, range(6)); y = Y.basis()
             sage: G = Y.submodule([y[0]-y[1], y[1]-y[2], y[2]-y[3]])
             sage: F.is_submodule(G)
-            Traceback (most recent call last):
-            ...
-            ValueError: other (=...) should be a submodule of the same ambient space
+            False
         """
         if other is self._ambient:
             return True
         if not (isinstance(self, SubmoduleWithBasis) and self.ambient() is other.ambient()):
-            raise ValueError("other (=%s) should be a submodule of the same ambient space" % other)
+            return False  # different ambient spaces
         if self not in ModulesWithBasis.FiniteDimensional:
             raise NotImplementedError("only implemented for finite dimensional submodules")
         if self.dimension() > other.dimension():  # quick dimension check