Abstract: Four kinds of cristrfuzzy variable threshold concepts are introduced in a fuzzy formal context and they form four kinds of variable threshold concept lattices respectively. And then four kinds of decision rule sets are obtained based on these lattices. Algorithms to inferences under different decision rule sets are established by an inclusion degrec,and total decision rules of all combinations among objects arc acquired. The decisions from the total decision rules are proved to be the lower approximated and the upper approximated decision sets,and the algorithms are accordant and consistent.

Key words: Variable threshold concept, Decision rule, Inference algorithm, Inclusion degree