Multi-fuzzy Rough Sets based on Implicators and Continuous t-norms

This paper extends the study of multi-fuzzy rough sets using an implicator and a continuous t-norm and thus introduces multi-fuzzy rough sets based on fuzzy logical connectives. In this constructive approach, a pair of lower and upper approximation operators determined by an implicator and a triangular norm is defined. The fundamental properties of these approximation operators are examined. Connections between multi-fuzzy relations and the newly constructed multi-fuzzy rough approximation operators are also established. The theory of multi-fuzzy rough sets is analysed using an operator oriented view in the later sections. The lower and upper approximation operators are characterized by axioms. Various axiom sets of lower and upper multi-fuzzy set theoretic operators guarantee the existence of different types of multi-fuzzy relations which produce the same operators.