static L<S> splitAtDoubleArrow_bothDirections(S s) {
  ret splitAtDoubleArrow_bothDirections(javaTok(s));
}

static L<S> splitAtDoubleArrow_bothDirections(L<S> tok) {
  L<S> l = splitAtDoubleArrow(tok);
  if (l(l) != 2) l = reversedList(splitAtDoubleLeftArrow(tok));
  ret l;
}