and true X X and false Y false if true X Y X if false X Y Y add 0 X X add s X Y s add X Y first 0 X nil first s X cons Y Z cons Y first X Z from X cons X from s X 2.2 from X from s X first s X cons Y Z first X Z add s X Y add X Y true add s X Y add X Y true s 1 1 1 and 2 0 false 0 0 true 0 0 if 3 0 0 0 0 from 1 0 first 2 0 nil 0 0 first 2 0 from 1 0 cons 2 0 if 3 0 add 2 1 0 add 2 0 and 2 0 first s X cons Y Z first X Z true s 1 1 and 2 0 false 0 0 true 0 0 if 3 0 0 0 0 from 1 0 first 2 2 0 nil 0 0 first 2 0 from 1 0 cons 2 2 1 if 3 0 add 2 0 add 2 0 and 2 0 from X from s X true Failed! NaTT certifiable-1.6