persistable sclass NLABlock {
  S text;   // original text
  LS lines; // same, split into lines
  Set<Entity> entities; // entities
  L<Line> parsedLines;

  sclass Line {
    S text;
    int index;
    Entity introducedEntity;
    L proposition; // fragments
    
    toString {
      ret joinWithSpace(proposition)
        + (introducedEntity == null ? "" : " => " + introducedEntity);
    }
  }

  sclass Entity extends Cluster {
    S definedInLine;
    
    *(S name, S *definedInLine) { addSynonym(name); }
  }
  
  *(S *text) {}
  
  bool isParsed() { ret parsedLines != null; }
  
  toString {
    ret !isParsed() ? text : lines_rtrim(parsedLines);
  }
  
  L<Line> propositions() {
    ret filter(parsedLines, line -> line.introducedEntity == null);
  }
}