diff --git a/src/fractal_btree_level.erl b/src/fractal_btree_level.erl
index ea480ad..4d861ad 100644
--- a/src/fractal_btree_level.erl
+++ b/src/fractal_btree_level.erl
@@ -81,7 +81,6 @@ reply({PID,Ref}, Reply) ->
 initialize(State) ->
     error_logger:info_msg("in ~p level=~p~n", [self(), State]),
 
-
     AFileName = filename("A",State),
     BFileName = filename("B",State),
     CFileName = filename("C",State),
@@ -120,82 +119,12 @@ initialize(State) ->
             end
     end.
 
-
-main_loop(State = #state{ a=undefined, b=undefined }) ->
-    Parent = plain_fsm:info(parent),
-    error_logger:info_msg("in main_loop~n", []),
-    receive
-        ?REQ(From, {lookup, _})=Msg ->
-            error_logger:info_msg("in main_loop, msg=~p~n", [Msg]),
-            case State#state.next of
-                undefined ->
-                    reply(From, notfound);
-                Next ->
-                    Next ! Msg
-            end,
-            main_loop(State);
-
-        ?REQ(From, {inject, FileName})=_Msg ->
-            error_logger:info_msg("in main_loop, msg=~p~n", [_Msg]),
-            AFileName = filename("A",State),
-            ok = file:rename(FileName, AFileName),
-            {ok, BT} = fractal_btree_reader:open(AFileName),
-            reply(From, ok),
-            main_loop(State#state{ a=BT });
-
-        ?REQ(From, close)=_Msg ->
-            error_logger:info_msg("in main_loop, msg=~p~n", [_Msg]),
-            reply(From, ok),
-            ok;
-
-        %% gen_fsm handling
-        {system, From, Req}=_Msg ->
-            error_logger:info_msg("in main_loop, msg=~p~n", [_Msg]),
-            plain_fsm:handle_system_msg(
-              From, Req, State, fun(S1) -> main_loop(S1) end);
-
-        {'EXIT', Parent, Reason}=_Msg ->
-            error_logger:info_msg("in main_loop, msg=~p~n", [_Msg]),
-            plain_fsm:parent_EXIT(Reason, State)
-    end;
-
-main_loop(State = #state{ a=BT1, b=undefined, next=Next }) ->
-    Parent = plain_fsm:info(parent),
-    error_logger:info_msg("in main_loop~n", []),
-    receive
-        ?REQ(From, {lookup, Key})=Req ->
-            case fractal_btree_reader:lookup(BT1, Key) of
-                {ok, deleted} ->
-                    reply(From, notfound);
-                {ok, _}=Reply ->
-                    reply(From, Reply);
-                notfound when Next =:= undefined ->
-                    reply(From, notfound);
-                notfound ->
-                    Next ! Req
-            end,
-            main_loop(State);
-
-        ?REQ(From, {inject, FileName}) ->
-            BFileName = filename("B",State),
-            ok = file:rename(FileName, BFileName),
-            {ok, BT2} = fractal_btree_reader:open(BFileName),
-            reply(From, ok),
-            {ok, MergePID} = begin_merge(State),
-            main_loop(State#state{ b=BT2, merge_pid=MergePID });
-
-        ?REQ(From, close) ->
-            fractal_btree_reader:close(BT1),
-            reply(From, ok),
-            ok;
-
-        %% gen_fsm handling
-        {system, From, Req} ->
-            plain_fsm:handle_system_msg(
-              From, Req, State, fun(S1) -> main_loop(S1) end);
-        {'EXIT', Parent, Reason} ->
-            plain_fsm:parent_EXIT(Reason, State)
-    end;
+check_begin_merge_then_loop(State=#state{a=BT1, b=BT2, merge_pid=undefined})
+  when BT1/=undefined, BT2 /= undefined ->
+    {ok, MergePID} = begin_merge(State),
+    main_loop(State#state{merge_pid=MergePID });
+check_begin_merge_then_loop(State) ->
+    main_loop(State).
 
 main_loop(State = #state{ next=Next }) ->
     Parent = plain_fsm:info(parent),
@@ -212,16 +141,23 @@ main_loop(State = #state{ next=Next }) ->
 	    end,
 	    main_loop(State);
 
+        ?REQ(From, {inject, FileName}) when State#state.b == undefined ->
+	    if State#state.a == undefined ->
+		    ToFileName = filename("A",State),
+		    SetPos = #state.a;
+	       true ->    
+		    ToFileName = filename("B",State),
+		    SetPos = #state.b
+	    end,
+	    ok = file:rename(FileName, ToFileName),
+	    {ok, BT} = fractal_btree_reader:open(ToFileName),
+	    reply(From, ok),
+	    check_begin_merge_then_loop(setelement(SetPos, State, BT));
+
         ?REQ(From, close) ->
-            fractal_btree_reader:close(State#state.a),
-            fractal_btree_reader:close(State#state.b),
-            MergePID = State#state.merge_pid,
-            if MergePID =:= undefined ->
-                    ok;
-               true ->
-                    erlang:exit(State#state.merge_pid, shutdown)
-            end,
-            %% TODO: stop merger, if any?
+            close_if_defined(State#state.a),
+            close_if_defined(State#state.b),
+            stop_if_defined(State#state.merge_pid),
             reply(From, ok),
             ok;
 
@@ -296,6 +232,13 @@ do_lookup(Key, [BT|Rest]) ->
 	notfound      -> do_lookup(Key, Rest)
     end.
 
+close_if_defined(undefined) -> ok;
+close_if_defined(BT)        -> fractal_btree_reader:close(BT).
+
+stop_if_defined(undefined) -> ok;
+stop_if_defined(MergePid=) when is_pid(MergePid) ->
+    erlang:exit(MergePid, shutdown).
+
 begin_merge(State) ->
     AFileName = filename("A",State),
     BFileName = filename("B",State),