Python assignment semantics vs Fortran

It's not clear (to me) how to map Python's assignment semantics (refcounting and everything) into Fortran. At the same time, doing something mildly smarter than just copying data all the time is required for decent performance on things like AB history shifts.

There are basically two possible routes:

• Smarter analysis
• An implementation of Python-like refcounting (without cycles, thankfully)