  In a real expert system, one may have unreliable, unconfident, conflicting
estimates of the value for a particular parameter. It is important for decision
making that the information present in this aggregate somehow find its way into
use. We cast the problem of representing and combining uncertain estimates as
selection of two kinds of functions, one to determine an estimate, the other
its uncertainty. The paper includes a long list of properties that such
functions should satisfy, and it presents one method that satisfies them.
