2. Iterate: Iterate over pairs of maxima x, y ∈ M L (G). Step 8 identifies a non-critical path between neighbouring regions by noting that the critical point is pushed right to the edge of the shared border of the regions (see path P BC in Fig. ). In order for two regions to be critically linked, the critical point must instead constitute a saddle point in the bulk of the shared boundary (as is the case for paths P AC and P AB in Fig. ).