__ __ X Y Z __ X __ Y Z __ X nil X __ nil X X U11 tt U12 tt U12 tt tt isNePal __ I __ P I U11 tt activate X X 2.2 __ __ X Y Z __ X __ Y Z __ __ X Y Z __ Y Z isNePal __ I __ P I U11 tt U11 tt U12 tt true isNePal __ I __ P I U11 tt false U11 tt U12 tt false __ __ X Y Z __ Y Z __ __ X Y Z __ X __ Y Z true U11 1 0 activate 1 0 activate 1 0 __ 2 1 0 isNePal 1 0 U12 1 0 U12 1 0 isNePal 1 0 nil 0 1 U11 1 0 tt 0 0 __ 2 1 2 1 NaTT certifiable-1.6