The special region of this PES here is the shoulder, Sh, where some NTs come close to each other, but do not intersect . The steepest descent from SP2 leads to the shoulder. To connect SP2 with the minimum, M, we have to find a direction between the blue singular NTs through VRI points X1 and X2. For example, this is fulfilled by the dashed red NT to direction (0.987, 0.163). Before M , the red NT moves together with the magenta NT to SP5. This means that the corridors before M and after M are different. Note that there is no bifurcation of the valley of M at the shoulder, Sh. The corresponding bifurcation points are X1 and X5, which are the boundary points for the corridor of the thick black NT from the minimum M to SP 1.