public static Stella_Object conjoinSentences(Cons sentences) {
    sentences = sentences.remove(Stella.NIL);
    if (sentences == Stella.NIL) {
      return (Stella.NIL);
    }
    else if (sentences.rest == Stella.NIL) {
      return (sentences.value);
    }
    else {
      sentences = Cons.cons(Logic.SYM_STELLA_AND, sentences);
      return (sentences);
    }
  }