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<Paper uid="C92-3144">
  <Title>THE FIRST BUC REPORT</Title>
  <Section position="6" start_page="0" end_page="0" type="concl">
    <SectionTitle>
5, Generative Capacity
</SectionTitle>
    <Paragraph position="0"> Somewhat misleadingly, we have avoided so far makhag a distinction between the context-free grammar format and context-free grammars. In actual fact, it is well-known that a unification-based grammar in the context-free format is not context-free unless the number of possible feature structures arising in all its possible derivations is finite. By the same token, the automata compiled by BU~ would not recognize a regular language if we did not constrain the possible feature structures that they give rise to. The separation of SDs from SCS allows ~IUG to avoid this problem. Since SDs are only used in unifiability tests and are never modified at run-time, they can be constrained in such a way that they yield a finite set of equivalence classes of feature structures. Moreover, carrying out SCs only affects the structures being built and cannot interfere with the trajectory through the automaton. Incidentally, this means that unification (but not unifiability tests!) may never fail. For that purpose, we use an associative, idempotent and commutative version of 'default unification' (see Bouma, 1990), which we are not going into here. The automaton produced by BU~ is, thus, actually finite-state. We consider this an extremely important benefit, if not the most important one, of separating SDs from SCs in a grammar-writing system.</Paragraph>
  </Section>
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