a__zeroscons0zerosa__andttXmarkXa__lengthnil0a__lengthconsNLsa__lengthmarkLmarkzerosa__zerosmarkandX1X2a__andmarkX1X2marklengthXa__lengthmarkXmarkconsX1X2consmarkX1X2mark00markttttmarknilnilmarksXsmarkXa__zeroszerosa__andX1X2andX1X2a__lengthXlengthXa__zerosa__andttXa__lengthnila__lengthconsNLmarkzerosmarkandX1X2marklengthXmarkconsX1X2mark0markttmarknilmarksXa__andX1X2a__lengthX2.1a__lengthconsNzerosa__lengthconsNLsa__lengthmarkLsa__lengthmarkzeros11markzerosa__zerossa__lengtha__zeros11a__zeroscons0zerossa__lengthcons0zerosN0sttt21.14unfold -fp -vpos -sc -fph