InfinityRing, UnsignedInfinityRing: Add is_field method

Author: Matthias Koeppe

src/sage/rings/infinity.py

@@ -592,6 +592,17 @@ def ngens(self):
         """
         return 1
 
+    def is_field(self, proof=True):
+        """
+        The unsigned infinity ring isn't a field.
+
+        EXAMPLES::
+
+            sage: UnsignedInfinityRing.is_field()
+            False
+        """
+        return False
+
     def fraction_field(self):
         """
         The unsigned infinity ring isn't an integral domain.
@@ -1010,6 +1021,17 @@ def __init__(self):
         """
         Ring.__init__(self, self, names=('oo',), normalize=False)
 
+    def is_field(self, proof=True):
+        """
+        The unsigned infinity ring isn't a field.
+
+        EXAMPLES::
+
+            sage: InfinityRing.is_field()
+            False
+        """
+        return False
+
     def fraction_field(self):
         """
         This isn't really a ring, let alone an integral domain.