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<Paper uid="W96-0403">
  <Title>Paraphrasing and Aggregating Argumentative Text Using Text Structure</Title>
  <Section position="2" start_page="0" end_page="21" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Many of the first NLG systems link their information structure to the corresponding linguistic resources either through predefined templates or via careful engineering for a specific application. Therefore their expressive power is restricted (see \[12\] for an extensive discussion). An increasing interest in more sophisticated microplanning techniques can be clearly observed \[12, 14\], however. In this paper, we first motivate the needs for paraphrasing and aggregation for the generation of argumentative texts, in particular of mathematical proofs, and then describe how our microplanning operations can be formulated in terms of Meteer's Text Structure.</Paragraph>
    <Paragraph position="1"> The work reported here is part of a fully implemented system called PRO VERB, which produces natural language proofs from proofs found by' automated reasoning systems \[7\]. First experiments with PRO VERB resulted in very mechanical texts due to the lack of microplanning techniques. According to our analysis, there are at least two linguistic phenomena that call for appropriate microplanning techniques.</Paragraph>
    <Paragraph position="2"> First, naturally occurring proofs contain paraphrases with respect to both rhetorical relations, as well as to logical functions or predicates. For instance, the derivation of B from A can be verbalized as: &amp;quot;Since A, B.&amp;quot; or as &amp;quot;A leads to B.&amp;quot; The logic predicate para(C1, C2), also, can be verbalized as: &amp;quot;Line C1 parallels line C2.&amp;quot; or as &amp;quot;The parallelism of the lines C1 and C2.&amp;quot; Second, without microplanning PROVERB generates text structured exactly mirroring the information structure of the proof and the formulae. This means that every step of derivation is translated into a separate sentence, and formulae are recursively verbalized. As an instance of the latter, the formula</Paragraph>
    <Paragraph position="4"> is verbalized as  &amp;quot;F is a set. F is a subset of G.&amp;quot; although the following is much more natural: &amp;quot;The set F is a subset of G.&amp;quot; Therefore, we came to the conclusion that an intermediate level of representation is necessary that allows flexible combinations of linguistic resources. It is worth pointing out that these techniques are required although the input information chunks are of clause size. Another requirement is that this intermediate representation is easy to control, since a mathematical text must conform to the syntactic rules of its sublanguage. In the next section, we first give a brief overview of PROVERB. Then we describe the architecture of our microplanner, and illustrate how Meteer's Text Structure can be adopted as our central representation. In Sec. 5 and 6 we describe the handling of paraphrases and aggregation rules, two of the major tasks of our microplanner.</Paragraph>
  </Section>
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