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<Paper uid="W94-0317">
  <Title>Planning Reference Choices for Argumentative Texts</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
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1 Introduction
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    <Paragraph position="0"> This paper describes how reference decisions are made in PROVERB, a system that verbalizes machine-found natural deduction (ND) proofs. A piece of argumentative text such as the proof of a mathematical theorem can be viewed as a sequence of derivations. Each such derivation is called a proof communicative act (PCA), following the viewpoint that speeches are actions. By reference choices we mean the explicitness of the verbalization of certain entities in the PCAs. Concretely, such decisions must be made for intermediate conclusions used as premises, as well as for the inference method. As an example, let us look at the PCA with the name Derive below:</Paragraph>
    <Paragraph position="2"> Here, Derived-Formula is filled by a new intermediate conclusion the current PCA aims to convey, which is derivable by applying the filler of Method, with the filler of Reasons as premises. While the new conclusion will usually be handed over unchanged for verbalization, there are alternatives for referring to both the Reasons and the Method. Depending on the discourse history, the following are two of the possible verbalizations:  1. (inference method omitted): &amp;quot;Since lu is the unit element of U, and u is an element of U, u* 1v = u.&amp;quot; 2. (reasons omitted): &amp;quot;According to the definition of unit element, u * 1v= u.&amp;quot;  Note that, an explicit reference to a premise or an inference method is not restricted to a nominal phrase, as opposed to the traditional subsequent references. Despite this difference, the choices to be made here have much in common with the choices of subsequent references discussed in more general frameworks \[Rei85, GS86, Da192\]: they depend on the availability of the object to be referred to in the context and are sensitive to the segmentation of the current context into an attentional hierarchy. Although this observation is widely agreed upon for subsequent references, no consensus about where the segment boundaries lie has been reached. In PROVERB, we attack this problem by viewing text generation as a combination of hierarchical planning \[Hov88, Moo89, Reigl, Dal92\] and local organization \[Sib90\]. Following \[GS86\], moreover, we assume that every posting of a new task by the hierarchical planning mechnism creates a new attentional unit. As a consequence, the attentional hierarchy is equivalent to the plan hierarchy. Based on this segmentation of context, PRO VERB makes reference choices according to a discourse theory adapted from that of Reichman \[Rei85, Hua90\].</Paragraph>
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