Consider the case in which query involves a single variable. Let X be the query variable (e.g. Cavity in previous slide) Let E be the set of evidence variable (e.g. Toothache), and let e be the observed values for them Let Y be the remaining unobserved variables (Catch). The query P(Xe) can be evaluated as (5).) P(Xe)=P(X,e)=yP(X,e,y) where the summation is over all possible y..