The Null Space of Fuzzy Inclusion Measures

In this article, some formal relationships between the different axiomatic definitions of inclusion measure are analyzed. In particular, the links between the different proposals about the null-space (the collection of pairs associated with a null degree of inclusion) are studied. Taking as starting point the well-known axiomatics of Kitainik and Sinha-Dougherty, we observe that other alternative proposals about the null-space are incompatible with both the null-space and the decomposition axioms of these authors. We also conclude that both the axiomatics of Kitainik and those of Sinha-Dougherty contain certain redundancies. Reduced equivalent lists of axioms are proposed.