from X cons X n__from s X first 0 Z nil first s X cons Y Z cons Y n__first X activate Z sel 0 cons X Z X sel s X cons Y Z sel X activate Z from X n__from X first X1 X2 n__first X1 X2 activate n__from X from X activate n__first X1 X2 first X1 X2 activate X X 2.2 sel s X cons Y Z sel X activate Z activate n__from X from X sel s X cons Y Z activate Z activate n__first X1 X2 first X1 X2 first s X cons Y Z activate Z true sel s X cons Y Z sel X activate Z true s 1 1 1 n__first 2 1 activate 1 1 1 n__from 1 1 1 activate 1 0 0 0 11293 sel 2 1 0 from 1 0 sel 2 0 first 2 0 nil 0 11297 first 2 1 2 3 from 1 0 cons 2 1 2 1 sel s X cons Y Z activate Z false first s X cons Y Z activate Z activate n__first X1 X2 first X1 X2 true s 1 1 1 n__first 2 1 2 1 activate 1 1 0 n__from 1 1 1 activate 1 1 0 0 0 1 sel 2 0 from 1 0 sel 2 0 first 2 1 2 0 nil 0 4 first 2 1 2 2 from 1 0 cons 2 1 2 1 activate n__from X from X false NaTT certifiable-1.6