#3917: don't allow {} as a set display.
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index 7931b95..974c500 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -223,7 +223,7 @@
displays by the lack of colons separating keys and values:
.. productionlist::
- set_display: "{" [`expression_list` | `comprehension`] "}"
+ set_display: "{" (`expression_list` | `comprehension`) "}"
A set display yields a new mutable set object, the contents being specified by
either a sequence of expressions or a comprehension. When a comma-separated
@@ -231,19 +231,8 @@
and added to the set object. When a comprehension is supplied, the set is
constructed from the elements resulting from the comprehension.
-
-Variables used in the generator expression are evaluated lazily in a separate
-scope when the :meth:`next` method is called for the generator object (in the
-same fashion as for normal generators). However, the :keyword:`in` expression
-of the leftmost :keyword:`for` clause is immediately evaluated in the current
-scope so that an error produced by it can be seen before any other possible
-error in the code that handles the generator expression. Subsequent
-:keyword:`for` and :keyword:`if` clauses cannot be evaluated immediately since
-they may depend on the previous :keyword:`for` loop. For example:
-``(x*y for x in range(10) for y in bar(x))``.
-
-The parentheses can be omitted on calls with only one argument. See section
-:ref:`calls` for the detail.
+An empty set cannot be constructed with ``{}``; this literal constructs an empty
+dictionary.
.. _dict: