U62ttslengthLzeroscons0U11ttttU21ttttU31ttttU41ttU42isNatIListU42ttttU51ttU52isNatListU52ttttU61ttU62isNatisNatttisNatU11isNatListisNatU21isNatisNatIListU31isNatListisNatIListttisNatIListU41isNatisNatListttisNatListU51isNatlengthnil0lengthconsNU61isNatList