diff --git a/moo/kernel/X11.moo b/moo/kernel/X11.moo
index e4a0c6b..53efb82 100644
--- a/moo/kernel/X11.moo
+++ b/moo/kernel/X11.moo
@@ -32,6 +32,10 @@ class X11(Object) [X11able,selfns.X11able3] from 'x11'
 	var event_loop_sem, event_loop_proc.
 	var llevent_blocks.
 
+method(#dual) abc { ^nil }
+method(#dual) def { ^nil }
+method(#dual) abc3 { ^nil }
+
 	interface X11able3
 	{
 		method(#dual) abc55.
diff --git a/moo/lib/bigint.c b/moo/lib/bigint.c
index 452eb6d..735686a 100644
--- a/moo/lib/bigint.c
+++ b/moo/lib/bigint.c
@@ -224,8 +224,6 @@ static int is_normalized_integer (moo_t* moo, moo_oop_t oop)
 
 MOO_INLINE static int is_bigint (moo_t* moo, moo_oop_t x)
 {
-	moo_oop_class_t c;
-
 	if (!MOO_OOP_IS_POINTER(x)) return 0;
 
 /* TODO: is it better to introduce a special integer mark into the class itself */
diff --git a/moo/lib/comp.c b/moo/lib/comp.c
index 268e6c2..36c1c86 100644
--- a/moo/lib/comp.c
+++ b/moo/lib/comp.c
@@ -3130,13 +3130,13 @@ static int method_exists (moo_t* moo, const moo_oocs_t* name)
 {
 	if (moo->c->cunit->cunit_type == MOO_CUNIT_INTERFACE)
 	{
-/* TODO: remove duplicate code */
+/* TODO: remove duplicate code between interface and class */
 		moo_cunit_interface_t* ifce = (moo_cunit_interface_t*)moo->c->cunit;
 
 		if (ifce->mth.type == MOO_METHOD_DUAL)
 		{
-			return moo_lookupdic(moo, ifce->self_oop->mthdic[0], name) != MOO_NULL ||
-			       moo_lookupdic(moo, ifce->self_oop->mthdic[1], name) != MOO_NULL;
+			return moo_lookupdic(moo, ifce->self_oop->mthdic[MOO_METHOD_INSTANCE], name) != MOO_NULL ||
+			       moo_lookupdic(moo, ifce->self_oop->mthdic[MOO_METHOD_CLASS], name) != MOO_NULL;
 		}
 		else
 		{
@@ -3153,8 +3153,8 @@ static int method_exists (moo_t* moo, const moo_oocs_t* name)
 		moo_cunit_class_t* cc = (moo_cunit_class_t*)moo->c->cunit;
 		if (cc->mth.type == MOO_METHOD_DUAL)
 		{
-			return moo_lookupdic(moo, cc->self_oop->mthdic[0], name) != MOO_NULL ||
-			       moo_lookupdic(moo, cc->self_oop->mthdic[1], name) != MOO_NULL;
+			return moo_lookupdic(moo, cc->self_oop->mthdic[MOO_METHOD_INSTANCE], name) != MOO_NULL ||
+			       moo_lookupdic(moo, cc->self_oop->mthdic[MOO_METHOD_CLASS], name) != MOO_NULL;
 		}
 		else
 		{
@@ -6657,11 +6657,11 @@ need to write code to collect string.
 
 	if (cc->mth.type == MOO_METHOD_DUAL)
 	{
-		if (!moo_putatdic(moo, cc->self_oop->mthdic[0], (moo_oop_t)name, (moo_oop_t)mth)) goto oops;
-		if (!moo_putatdic(moo, cc->self_oop->mthdic[1], (moo_oop_t)name, (moo_oop_t)mth)) 
+		if (!moo_putatdic(moo, cc->self_oop->mthdic[MOO_METHOD_INSTANCE], (moo_oop_t)name, (moo_oop_t)mth)) goto oops;
+		if (!moo_putatdic(moo, cc->self_oop->mthdic[MOO_METHOD_CLASS], (moo_oop_t)name, (moo_oop_t)mth)) 
 		{
 			/* 'name' is a symbol created of cc->mth.name. so use it as a key for deletion */
-			moo_deletedic (moo, cc->self_oop->mthdic[0], &cc->mth.name);
+			moo_deletedic (moo, cc->self_oop->mthdic[MOO_METHOD_INSTANCE], &cc->mth.name);
 			goto oops;
 		}
 	}
@@ -7820,10 +7820,52 @@ static int process_class_interfaces (moo_t* moo)
 	return 0;
 }
 
+struct ciim_t
+{
+	moo_oop_interface_t ifce;
+	moo_oop_class_t _class;
+	int mth_type;
+};
+typedef struct ciim_t ciim_t;
+
+static int on_each_method (moo_t* moo, moo_oop_dic_t dic, moo_oop_association_t ass, void* ctx)
+{
+	ciim_t* ciim = (ciim_t*)ctx;
+	moo_oocs_t name;
+
+	name.ptr = MOO_OBJ_GET_CHAR_SLOT(ass->key);
+	name.len = MOO_OBJ_GET_SIZE(ass->key);
+	ass = moo_lookupdic(moo, ciim->_class->mthdic[ciim->mth_type], &name);
+	if (!ass) 
+	{/* TODO: change error code */
+		moo_setsynerrbfmt (moo, MOO_SYNERR_ARGFLOOD, MOO_NULL, MOO_NULL, 
+			"%.*js not implementing %.*js>>%.*js",
+			MOO_OBJ_GET_SIZE(ciim->_class->name), MOO_OBJ_GET_CHAR_SLOT(ciim->_class->name),
+			MOO_OBJ_GET_SIZE(ciim->ifce->name), MOO_OBJ_GET_CHAR_SLOT(ciim->ifce->name),
+			name.len, name.ptr
+		);
+		return -1;
+	}
+
+/* TODO: check preamble flags in signature */
+	return 0;
+}
+
 static int class_implements_interface (moo_t* moo, moo_oop_class_t _class, moo_oop_interface_t ifce)
 {
-	
-	return 0;
+	ciim_t ciim;
+
+	ciim.ifce = ifce;
+	ciim._class = _class;
+	ciim.mth_type = MOO_METHOD_INSTANCE;
+	if (moo_walkdic(moo, ifce->mthdic[MOO_METHOD_INSTANCE], on_each_method, &ciim) <= -1) return 0;
+
+	ciim.ifce = ifce;
+	ciim._class = _class;
+	ciim.mth_type = MOO_METHOD_CLASS;
+	if (moo_walkdic(moo, ifce->mthdic[MOO_METHOD_CLASS], on_each_method, &ciim) <= -1) return 0;
+
+	return 1;
 }
 
 static int check_class_interface_conformance (moo_t* moo)
@@ -7833,15 +7875,7 @@ static int check_class_interface_conformance (moo_t* moo)
 
 	for (i = 0; i < cc->ifces.count; i++)
 	{
-		moo_oop_interface_t ifce = (moo_oop_interface_t)cc->ifces.ptr[i];
-		if (!class_implements_interface(moo, cc->self_oop, ifce))
-		{
-			moo_setsynerrbfmt (moo, MOO_SYNERR_ARGNAMEDUPL, &cc->fqn_loc, &cc->fqn, 
-				"%.*js not implementing interface %.*js", 
-				cc->fqn.len, cc->fqn.ptr,
-				MOO_OBJ_GET_SIZE(ifce->name), MOO_OBJ_GET_CHAR_SLOT(ifce->name));
-			return -1;
-		}
+		if (!class_implements_interface(moo, cc->self_oop, (moo_oop_interface_t)cc->ifces.ptr[i])) return -1;
 	}
 
 	return 0;
@@ -8283,11 +8317,11 @@ static int add_method_signature (moo_t* moo)
 
 	if (ifce->mth.type == MOO_METHOD_DUAL)
 	{
-		if (!moo_putatdic(moo, ifce->self_oop->mthdic[0], (moo_oop_t)name, (moo_oop_t)mth)) goto oops;
-		if (!moo_putatdic(moo, ifce->self_oop->mthdic[1], (moo_oop_t)name, (moo_oop_t)mth)) 
+		if (!moo_putatdic(moo, ifce->self_oop->mthdic[MOO_METHOD_INSTANCE], (moo_oop_t)name, (moo_oop_t)mth)) goto oops;
+		if (!moo_putatdic(moo, ifce->self_oop->mthdic[MOO_METHOD_CLASS], (moo_oop_t)name, (moo_oop_t)mth)) 
 		{
 			/* 'name' is a symbol created of ifce->mth.name. so use it as a key for deletion */
-			moo_deletedic (moo, ifce->self_oop->mthdic[0], &ifce->mth.name);
+			moo_deletedic (moo, ifce->self_oop->mthdic[MOO_METHOD_INSTANCE], &ifce->mth.name);
 			goto oops;
 		}
 	}
diff --git a/moo/lib/dic.c b/moo/lib/dic.c
index 4da0e88..22c9de6 100644
--- a/moo/lib/dic.c
+++ b/moo/lib/dic.c
@@ -62,7 +62,7 @@ static moo_oop_oop_t expand_bucket (moo_t* moo, moo_oop_oop_t oldbuc)
 	}
 
 	moo_pushtmp (moo, (moo_oop_t*)&oldbuc);
-	newbuc = (moo_oop_oop_t)moo_instantiate (moo, moo->_array, MOO_NULL, newsz); 
+	newbuc = (moo_oop_oop_t)moo_instantiate(moo, moo->_array, MOO_NULL, newsz); 
 	moo_poptmp (moo);
 	if (!newbuc) return MOO_NULL;
 
@@ -234,32 +234,32 @@ static moo_oop_association_t lookup (moo_t* moo, moo_oop_dic_t dic, const moo_oo
 moo_oop_association_t moo_putatsysdic (moo_t* moo, moo_oop_t key, moo_oop_t value)
 {
 	MOO_ASSERT (moo, MOO_CLASSOF(moo,key) == moo->_symbol);
-	return find_or_upsert (moo, (moo_oop_dic_t)moo->sysdic, (moo_oop_char_t)key, value);
+	return find_or_upsert(moo, (moo_oop_dic_t)moo->sysdic, (moo_oop_char_t)key, value);
 }
 
 moo_oop_association_t moo_getatsysdic (moo_t* moo, moo_oop_t key)
 {
 	MOO_ASSERT (moo, MOO_CLASSOF(moo,key) == moo->_symbol);
-	return find_or_upsert (moo, (moo_oop_dic_t)moo->sysdic, (moo_oop_char_t)key, MOO_NULL);
+	return find_or_upsert(moo, (moo_oop_dic_t)moo->sysdic, (moo_oop_char_t)key, MOO_NULL);
 }
 
 moo_oop_association_t moo_lookupsysdic (moo_t* moo, const moo_oocs_t* name)
 {
-	return lookup (moo, (moo_oop_dic_t)moo->sysdic, name);
+	return lookup(moo, (moo_oop_dic_t)moo->sysdic, name);
 }
 
 moo_oop_association_t moo_putatdic (moo_t* moo, moo_oop_dic_t dic, moo_oop_t key, moo_oop_t value)
 {
 	/*MOO_ASSERT (moo, MOO_CLASSOF(moo,key) == moo->_symbol);*/
 	MOO_ASSERT (moo, MOO_OBJ_IS_CHAR_POINTER(key));
-	return find_or_upsert (moo, dic, (moo_oop_char_t)key, value);
+	return find_or_upsert(moo, dic, (moo_oop_char_t)key, value);
 }
 
 moo_oop_association_t moo_getatdic (moo_t* moo, moo_oop_dic_t dic, moo_oop_t key)
 {
 	/*MOO_ASSERT (moo, MOO_CLASSOF(moo,key) == moo->_symbol); */
 	MOO_ASSERT (moo, MOO_OBJ_IS_CHAR_POINTER(key));
-	return find_or_upsert (moo, dic, (moo_oop_char_t)key, MOO_NULL);
+	return find_or_upsert(moo, dic, (moo_oop_char_t)key, MOO_NULL);
 }
 
 moo_oop_association_t moo_lookupdic (moo_t* moo, moo_oop_dic_t dic, const moo_oocs_t* name)
@@ -334,6 +334,29 @@ found:
 	return 0;
 }
 
+int moo_walkdic (moo_t* moo, moo_oop_dic_t dic, moo_dic_walker_t walker, void* ctx)
+{
+	moo_oow_t index, count;
+	moo_oop_association_t ass;
+
+	count = MOO_OBJ_GET_SIZE(dic->bucket);
+	for (index = 0; index < count; index++)
+	{
+		ass = (moo_oop_association_t)dic->bucket->slot[index];
+		if ((moo_oop_t)ass != moo->_nil)
+		{
+
+			MOO_ASSERT (moo, MOO_CLASSOF(moo,ass) == moo->_association);
+			/*MOO_ASSERT (moo, MOO_CLASSOF(moo,ass->key) == moo->_symbol);*/
+			MOO_ASSERT (moo, MOO_OBJ_IS_CHAR_POINTER(ass->key));
+
+			if (walker(moo, dic, ass, ctx) <= -1) return -1;
+		}
+	}
+
+	return 0;
+}
+
 moo_oop_dic_t moo_makedic (moo_t* moo, moo_oop_class_t _class, moo_oow_t size)
 {
 	moo_oop_dic_t dic;
@@ -342,11 +365,11 @@ moo_oop_dic_t moo_makedic (moo_t* moo, moo_oop_class_t _class, moo_oow_t size)
 	MOO_ASSERT (moo, MOO_CLASSOF(moo,_class) == moo->_class);
 	MOO_ASSERT (moo, MOO_CLASS_SPEC_NAMED_INSTVARS(MOO_OOP_TO_SMOOI(_class->spec)) >= MOO_DIC_NAMED_INSTVARS);
 
-	dic = (moo_oop_dic_t)moo_instantiate (moo, _class, MOO_NULL, 0);
+	dic = (moo_oop_dic_t)moo_instantiate(moo, _class, MOO_NULL, 0);
 	if (!dic) return MOO_NULL;
 
 	moo_pushtmp (moo, (moo_oop_t*)&dic);
-	tmp = moo_instantiate (moo, moo->_array, MOO_NULL, size);
+	tmp = moo_instantiate(moo, moo->_array, MOO_NULL, size);
 	moo_poptmp (moo);
 	if (!tmp) return MOO_NULL;
 
@@ -363,6 +386,5 @@ moo_oop_nsdic_t moo_makensdic (moo_t* moo, moo_oop_class_t _class, moo_oow_t siz
 {
 	MOO_ASSERT (moo, MOO_CLASSOF(moo,_class) == moo->_class);
 	MOO_ASSERT (moo, MOO_CLASS_SPEC_NAMED_INSTVARS(MOO_OOP_TO_SMOOI(_class->spec)) >= MOO_NSDIC_NAMED_INSTVARS);
-
-	return (moo_oop_nsdic_t)moo_makedic (moo, _class, size);
+	return (moo_oop_nsdic_t)moo_makedic(moo, _class, size);
 }
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index 13af13f..0a00ade 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -1049,6 +1049,13 @@ enum moo_bcode_t
 		(moo)->shuterr = shuterr; \
 	} while(0)
 
+typedef int (*moo_dic_walker_t) (
+	moo_t*                moo,
+	moo_oop_dic_t         dic,
+	moo_oop_association_t ass,
+	void*                 ctx
+);
+
 #if defined(__cplusplus)
 extern "C" {
 #endif
@@ -1234,6 +1241,13 @@ int moo_deletedic (
 	const moo_oocs_t* name
 );
 
+int moo_walkdic (
+	moo_t*            moo,
+	moo_oop_dic_t     dic,
+	moo_dic_walker_t  walker,
+	void*             ctx
+);
+
 moo_oop_dic_t moo_makedic (
 	moo_t*          moo,
 	moo_oop_class_t _class,