Let us assume there exist several expert systems using different infer
ence machines, working in parallel on the decision making problem from
the same area and supplying for a given object (patient) probabilitie
s of different diagnoses. The global results (i.e. number of errors) o
n some sample data set of patients determine which of the machines is
the best one. Is it possible, using the results (i.e. probabilities of
diagnoses for the given patient) of the other machines, to improve de
cision power of the best machine? A method, the supremal inference mac
hine or algorithm, is introduced attempting to combine different infer
ence machines with the help of the random variable ''error content in
decision'' whose density is constructed for different measures of cert
ainty. Experimental results on a case study from the area of rheumatol
ogy are given.