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<Paper uid="W91-0112">
  <Title>A GENERAL COMPUTATIONAL METHOD FOR GRAMMAR INVERSION</Title>
  <Section position="3" start_page="91" end_page="91" type="intro">
    <SectionTitle>
IN AND OUT ARGUMENTS IN LITERALS
</SectionTitle>
    <Paragraph position="0"> Literals in the grammar clauses can be marked for the &amp;quot;modes&amp;quot; in which they are used. When a literal is submitted to execution then those of its arguments which are bound at that time are called the &amp;quot;in&amp;quot; arguments. After the computation is complete, some of the previously unbound arguments may become bound; these are called the &amp;quot;out&amp;quot; arguments. For example, in concat(\[a,b\],\[c,d\],Z), which is used for list concatenation, the first two arguments are &amp;quot;in&amp;quot;, while the third is &amp;quot;out&amp;quot;. The roles are reversed when concat is used for decomposition, as in concat(X,Y,\[a,b,c,d\]). In the literal subject(A1,A2,NUM,P), taken from an English grammar, AI and A2 are input and output strings of words, NUM is the number of the subject phrase, and P is the final translation. When the grammar is used for parsing, the &amp;quot;in&amp;quot; argument is A1; the &amp;quot;out&amp;quot; arguments are A2, NUM and P; when it is used for generation, the &amp;quot;in&amp;quot; argument is P; the &amp;quot;out&amp;quot; arguments are A1 and NUM. In generation, A2 is neither &amp;quot;in&amp;quot; nor &amp;quot;out&amp;quot;. &amp;quot;In&amp;quot; and &amp;quot;out&amp;quot; status of arguments in a PROLOG program can be computed statically at compile time.</Paragraph>
    <Paragraph position="1"> The general algorithm has been described in (StrTalkowski, 1990c; Strzalkowski and Peng, 1990).</Paragraph>
  </Section>
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