Fix a bug in demo program

examples/demo.py

@@ -10,7 +10,7 @@ bset = (isl.BasicSet.universe(space)
         .add_constraint(isl.Constraint.ineq_from_names(space, {1: 5, "y": -1})))
 print("set 1 %s:" % bset)
 
-bset2 = isl.BasicSet("{[x, y] : x >= 0 and x < 5 and y >= 0 and y < x+4 }")
+bset2 = isl.BasicSet("{[x, y] : x >= 0 and x < 5 and y >= 0 and y < x+4 }", context=ctx)
 print("set 2: %s" % bset2)
 
 bsets_in_union = []