BDFL ruling: Add section on open issues and leave it at that

pep-0218.txt

@@ -121,6 +121,25 @@ Long-Term Proposal
        "ValueError", because set elements are neither keys nor values.
 
 
+Open Issues for the Long-Term Proposal
+
+    Earlier drafts of PEP 218 had only a single set type, but the
+    sets.py implementation in Python 2.3 has two, Set and
+    ImmutableSet.  The long-term proposal has a single built-in
+    conversion function, set(iterable); how should instances of a
+    built-in immutable set type be created?  Possibilities include a
+    second immutable_set() built-in, or perhaps the set() function
+    could take an additional argument,
+    e.g. set(iterable, immutable=True)?
+
+    The PEP proposes {1,2,3} as the set notation and {-} for the empty
+    set.  Would there be different syntax for an immutable and a
+    mutable set?  Perhaps the built-in syntax would only be for
+    mutable sets, and an immutable set would be created from a mutable
+    set using the appropriate built-in function,
+    e.g. immutable_set({1,2,3}).
+
+
 Short-Term Proposal
 
     In order to determine whether there is enough demand for sets to