// snlMatchX keeps existing matches

static boolean snlMatchX(S pat, S snl, Map<S, Lisp> matches) {
  ret snlMatchX_sub(snlToTree_cached(pat), snlToTree(snl), matches);
}

static boolean snlMatchX(Lisp pat, S snl, Map<S, Lisp> matches) {
  ret snlMatchX_sub(pat, snlToTree(snl), matches);
}

static boolean snlMatchX(S pat, Lisp snl, Map<S, Lisp> matches) {
  ret snlMatchX_sub(snlToTree_cached(pat), snl, matches);
}

static boolean snlMatchX(Lisp pat, Lisp snl, Map<S, Lisp> matches) {
  ret snlMatchX_sub(pat, snl, matches);
}

static boolean snlMatchX_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 snlMatchX_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 (!snlMatchX_sub(pat.get(i), snl.get(i), m))
      ret false;
      
  ret true;
}

static boolean snlMatchX_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;
}

Began life as a copy of #1002721