Define boolean algebras, and create and parse boolean expressions
Description
"boolean.py" is a small library implementing a boolean algebra. It defines
two base elements, TRUE and FALSE, and a Symbol class that can take on one of
these two values. Calculations are done in terms of AND, OR and NOT - other
compositions like XOR and NAND are not implemented but can be emulated with
AND or and NOT. Expressions are constructed from parsed strings or in Python.
Python 3 version.
