static L<Map<NLABlock.Entity>> nla_partialMappings(NLABlock b1, NLABlock b2) {
  Set<L> propsB = b2.propositionSet();

  L<Map<NLABlock.Entity>> out = new L;
  loop: for (Map<NLABlock.Entity> map : nla_allPossibleMappings(b1, b2)) {
    for (NLABlock.Line line : b1.propositionLines()) {
      L bProp = nla_translateLine(line, map);
      if (!propsB.contains(bProp))
        continue loop;
    }
    out.add(map);
  }
  ret out;
}