<?xml version="1.0" standalone="yes"?>
<Paper uid="P83-1004">
  <Title>Formal Constraints on Metarules*</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> Metagrammaticai formalisms that combine context-free phrase structure rules and metarules (MPS grammars) allow concise statement of generalizations about the syntax of natural languages. Unconstrained MPS grammars, tmfortunately, are not cornputationally &amp;quot;safe.&amp;quot; We evaluate several proposals for constraining them, basing our amae~ment on computational tractability and explanatory adequacy. We show that none of them satisfies both criteria, and suggest new directions for research on alternative metagrammatical formalisms.</Paragraph>
  </Section>
class="xml-element"></Paper>