sclass NLAMappedProp {
  L proposition;
  NLABlock.Line metBy;
  
  toString {
    ret "prop (" + renderFragments(proposition) + ") "
      + (metBy == null ? "unmet" : "met by (" + renderFragments(metBy.proposition) + ")");
  }
}

sclass NLAMapping {
  NLABlock src, dest;
  Map<NLABlock.Entity> entityMap;
  Map<NLABlock.Line, NLAMappedProp> propositionMap;
}

static L<NLAMapping> nla_partialMappingsWithFailures(NLABlock b1, NLABlock b2) {
  Map<L, NLABlock.Line> propsB = b2.propositionIndex();

  new L<NLAMapping> out;
  loop: for (Map<NLABlock.Entity> map : nla_allPossibleMappings(b1, b2)) {
    new NLAMapping mapping;
    mapping.src = b1;
    mapping.dest = b2;
    mapping.entityMap = map;
    mapping.propositionMap = new Map;
    for (NLABlock.Line line : b1.propositionLines()) {
      new NLAMappedProp mp;
      mp.proposition = nla_translateLine(line, map);
      mp.metBy = propsB.get(mp.proposition);
      mapping.propositionMap.put(line, mp);
    }
    out.add(mapping);
  }
  ret out;
}

Began life as a copy of #1028747