in reply to Re^3: recursive formula.
in thread recursive formula.

Yes, that's correct

Or, like rsteinke explained it much better than I can in the chatterbox:
"If P(r_1) is the probability of getting r_1, and P(r_1,r_2) is the probability of getting r_1 and r_2, then P() is the probability of anything at all happening (unconstrained), which is 1"