Finally, we take the infimums with T max on both sides of the second step conclusion, i.e., T(u, S 1 ∪ S 2 ) ∧ T max = T(u, S 1 ) ∧ T(u, S 2 ) ∧ T max , which means (u, S 1 ∪ S 2 ) = (u, S 1 ) ∧ (u, S 2 ) by the definition of .