static Map<S, Pair<S, SS>> mechMapCI_leftArrows_cache = synchroMap();

static SS mechMapCI_leftArrows(S listName) {
  Pair<S, SS> p = mechMapCI_leftArrows_cache.get(listName);
  S text = mechList_raw(listName);
  if (p != null && eq(p.a, text)) ret p.b;
  p = pair(text, parseDoubleLeftArrowMapCI(tlftj(text)));
  mechMapCI_leftArrows_cache.put(listName, p);
  ret p.b;
}