static L<S> replaceIC(L<S> l, S a, S b) {
  new L<S> l2;
  for i over l: {
    S s = l.get(i);
    l2.add(eqic(s, a) ? b : s);
  }
  ret l2;
}

static S replaceIC(S s, S a, S b) {
  ret s.replaceAll("(?i)" + patternQuote(a), quoteReplacement(b));
}