On the Negative Disjunction Property

Abstract

In the field of intermediate logics, the concept of the disjunction property (DP)  plays an important part. Lloyd Humberstone has drawn my attention to an analogious principle  called the Negative Disjunction Property ( NDP) which applies when the disjuncts involved are negated. The author investigates the NDP in the case of intermediate propositional logics.

Key words: intermediate logic, disjunction property, negative disjunction property, Heyting algebra, Jankov