Using eval with substitutions

[abhishek at ocf.berkeley.edu]

Thanks very much for all your suggestions - Peter, Duncan and Frederic.
It was a great help.

Incidentally the question arose while I was trying to solve the 2-nots
problem,
http://www.inwap.com/pdp10/hbaker/hakmem/boolean.html#item19

Part of my program takes a set of boolean expressions in 3 variables
and keeps concatenating them with 'and' and 'or' until all unique
functions have been found. Sometimes it is good to use substitutions
(though not required) to make the patterns apparent. Anyway, the
listing is here,

http://www.ocf.berkeley.edu/~abhishek/twonot3.py

Abhishek