--- a/src/rps3.erl	Sat Mar 08 23:36:15 2014 +0900
+++ b/src/rps3.erl	Sat Mar 08 23:37:19 2014 +0900
@@ -17,8 +17,8 @@
 handle_call({winning_hand, Hands}, _From, State) ->
     {reply, rps_rules:winning_hand(Hands, State), State};
 
-handle_call({why, H1, H2}, _From, State=#ruleinfo{why=Why}) ->
-    {reply, dict:fetch({H1, H2}, Why), State}.
+handle_call({why, H1, H2}, _From, State=#ruleinfo{}) ->
+    {reply, rps_rules:why(H1, H2, State), State}.
 
 handle_cast(_Msg, State) -> {noreply, State}.
 

--- a/src/rps5.erl	Sat Mar 08 23:36:15 2014 +0900
+++ b/src/rps5.erl	Sat Mar 08 23:37:19 2014 +0900
@@ -17,8 +17,8 @@
 handle_call({winning_hand, Hands}, _From, State) ->
     {reply, rps_rules:winning_hand(Hands, State), State};
 
-handle_call({why, H1, H2}, _From, State=#ruleinfo{why=Why}) ->
-    {reply, dict:fetch({H1, H2}, Why), State}.
+handle_call({why, H1, H2}, _From, State=#ruleinfo{}) ->
+    {reply, rps_rules:why(H1, H2, State), State}.
 
 handle_cast(_Msg, State) -> {noreply, State}.
 

--- a/src/rps_rules.erl	Sat Mar 08 23:36:15 2014 +0900
+++ b/src/rps_rules.erl	Sat Mar 08 23:37:19 2014 +0900
@@ -1,5 +1,5 @@
 -module(rps_rules).
--export([parse/1, winning_hand/2]).
+-export([parse/1, winning_hand/2, why/3]).
 -include("rps_rules.hrl").
 
 add_unique(Elem, List) ->
@@ -39,3 +39,10 @@
                 true -> Hand
             end
         end, undefined, HSet).
+
+why(H1, H2, State=#ruleinfo{}) when is_atom(H2) ->
+    atom_to_list(dict:fetch({H1, H2}, State#ruleinfo.why));
+
+why(H1, Hands, State=#ruleinfo{}) when is_list(Hands) ->
+    F = fun(H2) -> why(H1, H2, State) ++ " " ++ atom_to_list(H2) end,
+    atom_to_list(H1) ++ " " ++ string:join(lists:map(F, Hands), ", ").