static L<GazelleTree> gazelle_reasonWithPreprocessing(S content, O... _) {
  S userName = stringPar userName(_);
  GazelleEvalContext ctx = optPar ctx(_);
  if (ctx == null) ctx = gazelle_stdChatEvalContext();
  
  // preprocess
  
  L<GazelleTree> l1 = ll(GazelleTree(ctx, content));
  addAll(l1, dm_gazelle_reasonAboutChatInput_v2(userName, content, 
    paramsPlus(_, acceptablePurposes := litset('preprocess))));
  
  // TODO: uniquify lines?
  
  if (debug) print("Got " + n_entries(l1) + " after preprocessing.");
  
  new L<GazelleTree> l2;
  
  for (GazelleTree tree : l1)
    addAll(l2, dm_gazelle_reasonAboutChatInput_v2(userName, tree.line, _));
  
  ret l2;
}