diff --git a/ocaml/Random_variable.ml b/ocaml/Random_variable.ml
index b2124a5..2ebbaee 100644
--- a/ocaml/Random_variable.ml
+++ b/ocaml/Random_variable.ml
@@ -429,7 +429,7 @@ let merge ~create_key ?update_block_id ?update_value ?update_weight t =
         if (x>y) then 1
         else if (x<y) then -1
         else 0)
-    |>  List.rev_map (fun (x,y) -> y)
+    |>  List.rev_map snd
     |>  List.rev
   }
 
@@ -555,8 +555,9 @@ let ( /! ) = two_variable_operator
 let compress =
   merge
    ~create_key:(fun block -> 
-      Printf.sprintf "%s %10.10d" (Compute_node.to_string block.Block.compute_node)
-      (((Block_id.to_int block.Block.block_id)+1)/2))
+      Printf.sprintf "%s %10.10d %10.10d"
+        (Compute_node.to_string block.Block.compute_node) block.Block.pid
+        (((Block_id.to_int block.Block.block_id)+1)/2))
    ~update_block_id:(fun block_id -> 
       ((Block_id.to_int block_id)+1)/2
       |> Block_id.of_int )
@@ -678,6 +679,7 @@ let compress_files () =
          | Not_found -> true
        )
     |> List.rev_map (fun x -> dir_name^x)
+    |> List.rev
   in
 
   let out_channel_dir =