a b b x1 b a a x1 a a b x1 b b a x1 2.2 a b b x1 a a x1 a b b x1 a x1 a a b x1 a x1 true a a b x1 a x1 a b b x1 a x1 a b b x1 a a x1 true a 1 1 11798 b 1 1 11798 a 1 1 0 a b b x1 b a a x1 a a b x1 b b a x1 NaTT certifiable-1.6