active zeros mark cons 0 zeros active tail cons X XS mark XS active cons X1 X2 cons active X1 X2 active tail X tail active X cons mark X1 X2 mark cons X1 X2 tail mark X mark tail X proper zeros ok zeros proper cons X1 X2 cons proper X1 proper X2 proper 0 ok 0 proper tail X tail proper X cons ok X1 ok X2 ok cons X1 X2 tail ok X ok tail X top mark X top proper X top ok X top active X active 1 zeros 0 mark 1 cons 2 0 0 tail 1 proper 1 ok 1 top 1 INNERMOST ./TRS/TRCSR/inn/Ex4_7_77_Bor03_C.trs