diff --git a/src/node/shell/chain_traversal.ml b/src/node/shell/chain_traversal.ml
index 02f88ab17..6294aec07 100644
--- a/src/node/shell/chain_traversal.ml
+++ b/src/node/shell/chain_traversal.ml
@@ -132,3 +132,19 @@ let new_blocks ~from_block ~to_block =
   path ancestor to_block >>= function
   | None -> assert false
   | Some path -> Lwt.return (ancestor, path)
+
+let live_blocks block n =
+  let rec loop bacc oacc block n =
+    Block.all_operation_hashes block >>= fun hashes ->
+    let oacc =
+      List.fold_left
+        (List.fold_left
+           (fun oacc op -> Operation_hash.Set.add op oacc))
+        oacc hashes  in
+    let bacc = Block_hash.Set.add (Block.hash block) bacc in
+    if n = 0 then Lwt.return (bacc, oacc)
+    else
+      Block.predecessor block >>= function
+      | None -> Lwt.return (bacc, oacc)
+      | Some predecessor -> loop bacc oacc predecessor (pred n) in
+  loop Block_hash.Set.empty Operation_hash.Set.empty block n
diff --git a/src/node/shell/chain_traversal.mli b/src/node/shell/chain_traversal.mli
index 67680038f..2afafcd83 100644
--- a/src/node/shell/chain_traversal.mli
+++ b/src/node/shell/chain_traversal.mli
@@ -46,3 +46,11 @@ val new_blocks:
     (excluded) to [to_block] (included).  The function raises an
     exception when the two provided blocks do not belong the the same
     [net].  *)
+
+val live_blocks:
+  Block.t -> int -> (Block_hash.Set.t * Operation_hash.Set.t) Lwt.t
+(** [live_blocks b n] return a pair [(blocks,operations)] where
+    [blocks] is the set of arity [n], that contains [b] and its [n-1]
+    predecessors. And where [operations] is the set of operations
+    included in those blocks.
+ *)