Merge 123f276 into a829ca3

diofant · May 16, 2015 · b598777 · b598777
2 parents a829ca3 + 123f276
commit b598777
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Showing 2 changed files with 19 additions and 5 deletions.
diff --git a/sympy/sets/sets.py b/sympy/sets/sets.py
@@ -1336,12 +1336,12 @@ def flatten(arg):
         if len(args) == 0:
             raise TypeError("Intersection expected at least one argument")
 
+        args = list(ordered(args, Set._infimum_key))
+
         # Reduce sets using known rules
         if evaluate:
             return Intersection.reduce(args)
 
-        args = list(ordered(args, Set._infimum_key))
-
         return Basic.__new__(cls, *args)
 
     @property
@@ -1393,8 +1393,14 @@ def reduce(args):
         # all other sets in the intersection
         for s in args:
             if s.is_FiniteSet:
-                return s.func(*[x for x in s
-                    if all(other.contains(x) == True for other in args)])
+                args = [a for a in args if a != s]
+                res = s.func(*[x for x in s
+                             if all(other.contains(x) == True for other in args)])
+                unk = [x for x in s
+                      if any(other.contains(x) not in (True, False) for other in args)]
+                if unk:
+                    res += Intersection(*([s.func(*unk)] + args), evaluate=False)
+                return res
 
         # If any of the sets are unions, return a Union of Intersections
         for s in args:

diff --git a/sympy/sets/tests/test_sets.py b/sympy/sets/tests/test_sets.py
@@ -237,7 +237,15 @@ def test_intersect():
     assert Union(Interval(0, 1), Interval(2, 3)).intersect(S.EmptySet) == \
         S.EmptySet
     assert Union(Interval(0, 5), FiniteSet('ham')).intersect(FiniteSet(2, 3, 4, 5, 6)) == \
-        FiniteSet(2, 3, 4, 5)
+        Union(FiniteSet(2, 3, 4, 5),
+              Intersection(FiniteSet(6), Union(Interval(0, 5),
+                                               FiniteSet('ham'))))
+
+    # issue 8217
+    assert Intersection(FiniteSet(x), FiniteSet(y)) == \
+        Intersection(FiniteSet(x), FiniteSet(y), evaluate=False)
+    assert FiniteSet(x).intersect(S.Reals) == \
+        Intersection(S.Reals, FiniteSet(x), evaluate=False)
 
     # tests for the intersection alias
     assert Interval(0, 5).intersection(FiniteSet(1, 3)) == FiniteSet(1, 3)