Dung's semantics satisfy attack removal monotonicity

We show that preferred, stable, complete and grounded semantics satisfy attack removal monotonicity. This means that if an attack from b to a is removed, the status of a cannot worsen, e.g. if a was skeptically accepted, it cannot become rejected

Belief systems for persuasive discourse planning

This thesis is concerned with the problem of construction of the logical structure of a persuasive discourse. A persuasive discourse can be defined as a monodirectional form of communication, generated by a speaker in order to convince a hearer about the validity (or fallacy) of a specific belief The construction of the structure of a persuasive discourse is realized, in this work, through the adoption of two basic elements: a belief system and a planning system. The planning system is used as a tool for the automatic generation of the discourse structure (or plan), obtained through the decomposition of the assigned (communicative) goals of persuasion, aimed at producing specific effects on the hearer’s beliefs. The belief system is adopted in order to endow the planning process with a formal language of beliefs for the representation of such goals, and with the mechanisms which govern the propagation of their (expected) effects on the rest of the hearer's belief state. The main results presented consist of the formalization of a paradigm for specification of belief systems, and of a method — whose correctness is formally proved — for their integration with planning systems. The formalization of a belief system for discourse structure representation (defined in accordance with the theoretical paradigm) is also given, together with the description of its implementation and integration with a specific planner, which resulted in the actual completion of a system for the automatic generation of persuasive discourse plans