diff --git a/sys/living/comm.h b/sys/living/comm.h
index 064113a..500641a 100644
--- a/sys/living/comm.h
+++ b/sys/living/comm.h
@@ -97,9 +97,11 @@
 #ifndef __LIVING_COMM_H_PROTO__
 #define __LIVING_COMM_H_PROTO__
 
-public varargs int ReceiveMsg(string msg, int msg_type, string msg_action,
-                              string msg_prefix, object origin);
-public int ReceiveNotify(string msg, string action = 0);
+protected string comm_guess_action();
+public varargs int ReceiveMsg(string msg, int msg_type = 0,
+    string msg_action = comm_guess_action(), string msg_prefix = 0,
+    object origin = previous_object());
+public int ReceiveNotify(string msg, string action = comm_guess_action());
 
 #endif // __LIVING_COMM_H_PROTO__