normalize shebang lines to #!/usr/bin/env python
diff --git a/Demo/turtle/tdemo_yinyang.py b/Demo/turtle/tdemo_yinyang.py
index 47b8b2f..04dd758 100644
--- a/Demo/turtle/tdemo_yinyang.py
+++ b/Demo/turtle/tdemo_yinyang.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python
+#!/usr/bin/env python
 """       turtle-example-suite:
 
             tdemo_yinyang.py