from X cons X from s X sel 0 cons X Y X sel s X cons Y Z sel X Z 2.2 from X from s X sel s X cons Y Z sel X Z true sel s X cons Y Z sel X Z true s 1 1 0 0 0 sel 2 2 0 from 1 0 sel 2 0 from 1 0 cons 2 2 1 from X from s X true Failed! NaTT certifiable-1.6