forwarded fix in permutation to almost exact

Code/hull_almost_exact.cpp

@@ -120,7 +120,7 @@ size_t leftmost(const std::vector<vec>& points) {
   size_t min =  0 ;
   //iterato on all the points
   for(size_t i = 1; i < points.size(); ++i) {
-    if(points[i].x < points[min].x) {
+    if(points[i].lexicoinf(points[min])) {
       //update the leftmost
       min = i ;
     }