static SS ai_toPresentTense_map = litcimap(
  "was", "is",
  "went", "go",
  "had", "have",
  "said", "say",
  "did", "do");

static S ai_toPresentTense(S s) {
  L<S> tok = defaultTok(s);
  for (int i = 1; i < l(tok); i += 2) {
    S x = ai_toPresentTense_map.get(tok.get(i));
    if (x != null) tok.set(i, x);
  }
  ret join(tok);
}