static NLABlock nla_simplifyIntroductions(S text) {
  ret nla_simplifyIntroductions(nla_parse(text));
}

static NLABlock nla_simplifyIntroductions(NLABlock nla) {
  nla_parse(nla);
  for (NLABlock.Line line : nla.introductions()) {
    // simplify introduction
    line.proposition = frag("var *", line.introducedEntity);
    
    // introduce a new proposition
    NLABlock.Line prop = nla.new Line;
    prop.proposition
      // = frag("* is *", line.introducedEntity, line.introducedEntity.firstSynonym());
      = frag("* is " + line.introducedEntity.firstSynonym(), line.introducedEntity);
    nla.parsedLines.add(line.index()+1, prop);
  }
  ret nla;
}