static boolean snlMatch(S pat, S snl, Map<S, Lisp> matches) {

  matches.clear();

  ret snlMatch_sub(snlToTree_cached(pat), snlToTree(snl), matches);

}

static boolean snlMatch(Lisp pat, S snl, Map<S, Lisp> matches) {

  matches.clear();

  ret snlMatch_sub(pat, snlToTree(snl), matches);

}

static boolean snlMatch(S pat, Lisp snl, Map<S, Lisp> matches) {

  matches.clear();

  ret snlMatch_sub(snlToTree_cached(pat), snl, matches);

}

static boolean snlMatch(Lisp pat, Lisp snl, Map<S, Lisp> matches) {

  matches.clear();

  ret snlMatch_sub(pat, snl, matches);

}

static boolean snlMatch_sub(Lisp pat, Lisp snl, Map<S, Lisp> m) {

  if (pat == null || snl == null) ret false;

  if (pat.isA("*"))

    ret true;

  if (startsWithUpperCase(pat.head))

    ret snlMatch_putMatch(m, pat.head, snl);

  if (neq(pat.head, snl.head)) ret false;

  // heads identical, proceed to children

  int n = pat.size();

  if (n != snl.size()) ret false;

  for (int i = 0; i < n; i++)

    if (!snlMatch_sub(pat.get(i), snl.get(i), m))

      ret false;

  ret true;

}

static boolean snlMatch_putMatch(Map<S, Lisp> matches, S key, Lisp val) {

  if (matches.containsKey(key) && neq(matches.get(key), val))

    fail("multi-matching not implemented");

  matches.put(key, val);

  ret true;

}