wip demo self-crossing: it's now incorrectly mutating things

IV/notes.txt

@@ -48,12 +48,18 @@ but they will be eliminated by joining A and B anyway.
 Also, there is another way to remove self-crossing, without removing most of
 the bend. E.g. from:
 
-  \  \
+  \  /
   B\ |      __
    | |     /  \
    | |____/A  |
    \__________|
 
+Instead of:
+
+  \  /
+   \/ A'
+  B
+
 To:
 
   \  \_

IV/wm.sql

@@ -234,6 +234,14 @@ begin
       --   bends[i] = append(bends[i], multi[2][2..n])
       --   remove bends from bends[i+1] to bends[j] inclusive.
 
+      if j < i then
+        bends[j] = st_geometryn(multi, 1);
+        bends[j] = st_setpoint(bends[j], st_npoints(bends[j])-1, st_pointn(bends[i], st_npoints(bends[i])));
+        bends = bends[1:j] || bends[i+1:array_length(bends, 1)];
+      else
+        --
+      end if;
+
     end loop;
 
   end loop;