nats cons 0 n__incr nats pairs cons 0 n__incr odds odds incr pairs incr cons X XS cons s X n__incr activate XS head cons X XS X tail cons X XS activate XS incr X n__incr X activate n__incr X incr X activate X X 2.2 tail cons X XS activate XS activate n__incr X incr X incr cons X XS activate XS nats nats odds incr pairs pairs odds odds pairs true odds pairs pairs odds true Failed! NaTT certifiable-1.6