--- a/python/moving.py	Fri Aug 07 13:07:53 2015 -0400
+++ b/python/moving.py	Mon Aug 10 01:06:59 2015 -0400
@@ -78,12 +78,13 @@
         else:
             return None
 
-def unionIntervals(intervals):
-    'returns the smallest interval containing all intervals'
-    inter = intervals[0]
-    for i in intervals[1:]:
-        inter = Interval.union(inter, i)
-    return inter
+    @classmethod
+    def unionIntervals(cls, intervals):
+        'returns the smallest interval containing all intervals'
+        inter = cls(intervals[0].first, intervals[0].last)
+        for i in intervals[1:]:
+            inter = cls.union(inter, i)
+        return inter
 
 
 class TimeInterval(Interval):