diff --git a/src/graphics/graphics.c b/src/graphics/graphics.c
index 6b4985b..b641468 100644
--- a/src/graphics/graphics.c
+++ b/src/graphics/graphics.c
@@ -638,7 +638,7 @@ static inline int create_arrow (int arrows_nb,
 }
 
 static inline int erase_arrow (int arrows_nb, int arrow_address_in_list,
-                               int site, int x, int y, int z,
+                               GLuint site, GLint x, GLint y, GLint z,
                                int console)
 {
     if (arrows_nb == 0) assert (buffer_lines_size == buffer_lines_0_arrow); //   ?
@@ -661,16 +661,15 @@ static inline int erase_arrow (int arrows_nb, int arrow_address_in_list,
 
 
         if (console) printf("in erase_arrow() : arrows_nb decreases from %d to %d.   the erased arrow was at address : %d\n\
-                     : arrows_ptr[%d].site (value: %d) was replaced by %d  (%d was the value of the last arrow.site)\n",\
-            arrows_nb + 1, arrows_nb, arrow_address_in_list, arrow_address_in_list, \
-                            mem, arrows_ptr[arrows_nb].site, arrows_ptr[arrows_nb].site);
+                 : arrows_ptr[%d].site (value: %d) was replaced by arrows_ptr[%d].site (value: %d)\n",\
+            arrows_nb + 1, arrows_nb, arrow_address_in_list, arrow_address_in_list, mem, arrows_nb, arrows_ptr[arrows_nb].site);
     }
 
-        for (long i = 0 + arrow_address_in_list * 6; i < 6 + arrow_address_in_list * 6; i++)
-            buffer_vertex_origin [buffer_vertex_0_arrow + i] = buffer_vertex_origin [buffer_vertex_size - 6 + i];
+    for (long i = 0 + arrow_address_in_list * 6; i < 6 + arrow_address_in_list * 6; i++)
+        buffer_vertex_origin [buffer_vertex_0_arrow + i] = buffer_vertex_origin [buffer_vertex_size - 6 + i];
 
-        for (long i = 0 + arrow_address_in_list * 6; i < 6 + arrow_address_in_list * 6; i++)
-            buffer_colors_origin [buffer_colors_0_arrow + i] = buffer_colors_origin [buffer_colors_size - 6 + i];
+    for (long i = 0 + arrow_address_in_list * 6; i < 6 + arrow_address_in_list * 6; i++)
+        buffer_colors_origin [buffer_colors_0_arrow + i] = buffer_colors_origin [buffer_colors_size - 6 + i];
 
     buffer_vertex_size -= 6;   // <<<   l'inverse de ce qui est fait dans : graphics_write_vertex()
     buffer_colors_size -= 6;   // <<<   l'inverse de ce qui est fait dans : graphics_write_colors()
@@ -690,6 +689,7 @@ static inline int erase_arrow (int arrows_nb, int arrow_address_in_list,
     /* else                      perror("In graphics.erase_arrow(), can't re_allocate for arrows lines buffer.\n"); */
 
     if (1) print_arrows_array (arrows_ptr, arrows_nb, 0);
+    if (1) printf("\n");
 
     return arrows_nb;
 }
@@ -701,6 +701,9 @@ static inline int set_arrow (struct arrow_t *arrows_ptr, int arrows_nb, int spac
 {
     int address = -1, current_weight = -1;
 
+    printf("in set_arrow (begin)   arrows_nb = %d    requested site: %d    >   ", arrows_nb, site);
+    for (int i = 0; i < arrows_nb; i++) {printf(" [%d] = %d    ", i, arrows_ptr[i].site); if (site       ==  arrows_ptr[i].site) break;}
+
     for (int i = 0; i < arrows_nb; i++)
         if ((site       ==  arrows_ptr[i].site)
         &&  (arrow_x    ==  arrows_ptr[i].x)
@@ -712,6 +715,10 @@ static inline int set_arrow (struct arrow_t *arrows_ptr, int arrows_nb, int spac
             break;
         }
     assert (address <= arrows_nb);
+    if (address == -1 && requested_weight  > 0)              printf("    >>    create_arrow() at site %d\n", site);
+    if (address >=  0 && requested_weight == 0)              printf("    >>    erase_arrow() at site %d\n", site);
+    if (address >=  0 && current_weight != requested_weight) printf("    >>    rewrite_arrow() at site %d\n", site);
+    if (address == -1 && requested_weight == 0)              printf("    >>    no operation\n");
 
     if (address == -1 && requested_weight  > 0)
         return create_arrow  (arrows_nb, space_X, space_Y, space_Z, requested_weight, site, arrow_x, arrow_y, arrow_z, console);
@@ -779,11 +786,11 @@ void main_test_graphics (void)
     /* else for (int i = 0; i < 1; i++) ; */
     arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 0, 0, 0, 0, 1);
     arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 1, 0, 0, 0, 1);
-    arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 2, 0, 0, 0, 1);
-    arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 3, 0, 0, 0, 1);
-    arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 4, 0, 0, 0, 1);
-    arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 5, 0, 0, 0, 1);
-    arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 6, 0, 0, 0, 1);
+    /* arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 2, 0, 0, 0, 1); */
+    /* arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 3, 0, 0, 0, 1); */
+    /* arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 4, 0, 0, 0, 1); */
+    /* arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 5, 0, 0, 0, 1); */
+    /* arrows_nb = set_arrow (arrows_ptr, arrows_nb, 1, 1, 1, 0, 6, 0, 0, 0, 1); */
 
     if (randomize) print_user_choices(arrows_ptr, max_arrows_nb, arrows_nb, space_X, space_Y, space_Z, 1, 0);