not have a math vocabulary.
+-------------------------------+------------+---------------------------------+
| Operation | Equivalent | Result |
+===============================+============+=================================+
-| ``len(s)`` | | cardinality of set *s* |
+| ``len(s)`` | | number of elements in set *s*
+| | | (cardinality) |
+-------------------------------+------------+---------------------------------+
| ``x in s`` | | test *x* for membership in *s* |
+-------------------------------+------------+---------------------------------+
.. describe:: len(s)
- Return the cardinality of set *s*.
+ Return the number of elements in set *s* (cardinality of *s*).
.. describe:: x in s