static L<Proposition> ai_indentedLinesPropositions(S s) {
  LS lines = lines(s);
  new L<Proposition> out;
  for i over lines:
    out.add(withReasoning("line \*i+1*/ is " + (isIndented(lines.get(i)) ? "" : "not ") + "indented", "line \*i+1*/ is " + quote(lines.get(i))));
  ret out;
}