static L<GazelleTree> gazelle_searchTreeUpwardsForDefinitions(S word, GazelleTree tree) {
  if (tree == null || empty(word)) null;
  fS prefix = word + " = ";
  ret gazelle_searchTreeUpwards_all(func(GazelleTree t) -> bool {
    swic(t.line, prefix)
  }, tree);
}