Although STs already capture the aspect dependency induced by their varying roots, the path criterion is still not met.
we generalize the concept of a ST to that of a cohesion tree as follows: First, we observe that the construction of STs uses two types of order relations: the first, let it call ≤ 1 x , determines the order of the nodes inserted dependent on root x; the second, let it call ≤ 2 y , varies with node y to be inserted and determines its predecessor.