Can you construct a story in your class assignment example of why the
probability you are forced to teach class R would be something we would
want to be able to query the system about?
Let me try,
I told the school principal I hate to teach class R.
This bastard always assigns to me the classes that I hate
and, if he does it this time, I am going to shoot him.
However, if he does it because there is no other
alternative, I am going to forgive him.
Thus,
Pr(R) = chances I will be assigned R
Bel(R) = chances that the assignment (of R to me) will be inevitable.
Pr(R)-Bel(R) = chances I will have to shoot him.
========Judea