sS arbitraryVarsToStars(S s, Set<S> vars, LS varNames_out) {
  if (empty(vars)) ret s;
  LS tok = javaTok(s);
  LS tok2 = arbitraryVarsToStars(tok, vars, varNames_out);
  ret tok == tok2 ? s : join(tok2);
}

static LS arbitraryVarsToStars(LS tok, Set<S> vars, LS varNames_out) {
  if (empty(vars)) ret tok;
  LS tok2 = null;
  int n = l(tok);
  for i to n: {
    S t = tok.get(i);
    if (odd(i) && vars.contains(t)) {
      listAdd(varNames_out, t);
      if (tok2 == null) tok2 = cloneSubList(tok, 0, i);
      tok2.add("*");
    } else
      if (tok2 != null) tok2.add(t);
  }
  ret tok2 != null ? tok2 : tok;
}

Began life as a copy of #1010854