static L<Int> singleEllipsisMatchIC_splitIndices(S pat, S s) {
  int i = indexOf(pat, "...");
  if (i < 0) null;
  if (!regionMatchesIC(s, 0, pat, 0, i)) null;
  int lSuffix = l(pat)-(i+3);
  if (!regionMatchesIC(s, l(s)-lSuffix, pat, i+3, lSuffix)) null;
  ret ll(i, l(s)-lSuffix);
}