Max-Mim Chaining of Weighted Causal Assertions is Loop Free

If a system uses assertions of the general form x causes y, (e.g. MYCIN rules) then loop situations in which X1 causes X2, X2 causes X3, ...., Xn causes X1, are, intuitively, best avoided. If an assertion has an attached confidence weight, as in x (0.8)-causes y, then one can choose to say that the confidence in a chain of such assertions is as strong as the weakest link in the chain. If there are several chains of assertions from X to Z, then one can choose to say that X causes Z with a confidence equal to that of the strongest chain. From these choices, it follows that the confidence that X causes Z corresponds to a loop-free chain of assertions. This is true even if there are chains from X to Z with common subchains and loops within loops. An algorithm for computing the confidence is described.