These functions, which I had to implement in Python 2.2, are now
available in standard Python.

Patched bug: enumeration_joint_ask gave wrong answers when the query variable overlaps the evidence.

Fixed: enumerate_joint_ask would raise KeyError on a combo of var values that didn't happen to be set. Though maybe this is too lenient, catching KeyError in ProbDist.__getitem__? (instead of in JointProbDist)

Agent.__init__ now takes a program parameter. A few more nonlocal-state-variable problems found and fixed. One agent program rewritten as a callable instance since it uses both state variables and abstract methods.

functions condprob and condsamp.

Added function event_values.

In BayesNet class, initialize instance variable evidence.

Simplified comments.