static void thoughtSpaceDone(AbstractThoughtSpace ts) {
  if (ts != currentThoughtSpace())
    fail("Can't close thought space, not current: " + ts);
  thoughtSpaceDone();
}

static void thoughtSpaceDone() {
  AbstractThoughtSpace ts = currentThoughtSpace();
  if (ts instanceof ActualThoughtSpace)
    thoughtSpace(ts.parent);
  else
    print("thoughtSpaceDone without thought space");
}