f n__a n__b X f X X X c a c b a n__a b n__b activate n__a a activate n__b b activate X X 2.2 activate n__a a f n__a n__b X f X X X activate n__b b c a c b true c b false c a false activate n__b b false f n__a n__b X f X X X true Failed! NaTT certifiable-1.6