persistable sclass NLABlock {

  S text;   // original text

  LS lines; // same, split into lines

  Set<Entity> entities; // entities

  L<Line> parsedLines;

  class Line {

    S text;

    Entity introducedEntity;

    L proposition; // fragments

    *() {}

    *(S *text) {}

    *(S *text, L *proposition) {}

    toString {

      ret joinWithSpace(proposition)

        + (introducedEntity == null ? "" : " => " + introducedEntity);

    }

    int index() { ret parsedLines.indexOf(this); }

  }

  sclass Entity extends Cluster {

    Line definedInLine;

    O userObject;

    *(S name, Line *definedInLine) {

      this(name);

      if (definedInLine != null) definedInLine.introducedEntity = this;

    }

    *(S name) { addSynonym(name); }

  }

  *(S *text) {}

  bool isParsed() { ret parsedLines != null; }

  toString {

    ret !isParsed() ? text : lines_rtrim(parsedLines);

  }

  L<Line> introductions() {

    ret filter(parsedLines, line -> line.introducedEntity != null);

  }

  L<Line> propositionLines() {

    ret filter(parsedLines, line -> line.introducedEntity == null);

  }

  Set<L> propositionSet() {

    ret collectAsSet proposition(propositionLines());

  }

  Map<L, Line> propositionIndex() {

    ret indexByField proposition(propositionLines());

  }

}