and tt X __ __ X Y Z __ X __ Y Z __ X nil X __ nil X X isList isNeList isList tt isList and isList isNeList isQid isNeList and isList isNeList and isNeList isNePal isQid isNePal and isQid isPal isNePal isPal tt isQid tt 2.2 NaTT certifiable-1.6