a__first 0 X nil a__first s X cons Y Z cons mark Y first X Z a__from X cons mark X from s X mark first X1 X2 a__first mark X1 mark X2 mark from X a__from mark X mark 0 0 mark nil nil mark s X s mark X mark cons X1 X2 cons mark X1 X2 a__first X1 X2 first X1 X2 a__from X from X 2.2 mark cons X1 X2 mark X1 mark s X mark X mark first X1 X2 mark X2 mark first X1 X2 a__first mark X1 mark X2 a__from X mark X mark from X a__from mark X a__first s X cons Y Z mark Y mark first X1 X2 mark X1 mark from X mark X true mark from X mark X mark first X1 X2 mark X1 a__first s X cons Y Z mark Y mark from X a__from mark X mark first X1 X2 mark X2 mark s X mark X a__from X mark X mark first X1 X2 a__first mark X1 mark X2 mark cons X1 X2 mark X1 true s 1 1 1 a__from 1 1 1 a__first 2 1 2 0 a__from 1 1 2 mark 1 1 0 0 0 29604 from 1 1 2 nil 0 11798 mark 1 1 0 first 2 1 2 1 a__first 2 1 2 1 cons 2 1 2 mark first X1 X2 a__first mark X1 mark X2 mark s X s mark X a__first 0 X nil a__from X cons mark X from s X mark from X a__from mark X a__first X1 X2 first X1 X2 mark nil nil a__from X from X mark cons X1 X2 cons mark X1 X2 mark 0 0 a__first s X cons Y Z cons mark Y first X Z NaTT certifiable-1.6