In dense rule bases where the observation usually overlaps with severa
l antecedents in the rule base, various algorithms are used for approx
imate reasoning and control. If the antecedents are located sparsely,
and the observation does not overlap as a rule with any of the anteced
ents, function approximation techniques combined with the Resolution P
rinciple lead to applicable conclusions. This kind of approximation is
possible only if a new concept of ordering and distance, i.e. a metri
c in the state space, and a partial ordering among convex and normal f
uzzy sets (CNF sets) is introduced. So, the fuzzy distance of two CNF
sets can be defined, and by this distance, closeness and similarity of
CNF sets, as well.