diff --git a/moo/kernel/Collect.moo b/moo/kernel/Collect.moo
index d1638ab..4305d6b 100644
--- a/moo/kernel/Collect.moo
+++ b/moo/kernel/Collect.moo
@@ -76,6 +76,29 @@ class(#pointer) Array(Collection)
 	{
 		0 priorTo: (anArray basicSize) do: [:i | self at: i put: (anArray at: i) ].
 	}
+
+	method = anArray
+	{
+		| size i |
+		if (self class ~~ anArray class) { ^false }.
+
+		size := self size.
+		if (size ~~ anArray size) { ^false }.
+
+		i := 0.
+		while (i < size)
+		{
+			if ((self at: i) ~= (anArray at: i)) { ^false }.
+			i := i + 1.
+		}.
+
+		^true.
+	}
+
+	method ~= anArray
+	{
+		^(self = anArray) not
+	}
 }
 
 ## -------------------------------------------------------------------------------
diff --git a/moo/kernel/Process.moo b/moo/kernel/Process.moo
index 9c80d6f..deaaae7 100644
--- a/moo/kernel/Process.moo
+++ b/moo/kernel/Process.moo
@@ -62,46 +62,11 @@ class Semaphore(Object)
 
 	var(#get,#set) _group := nil.
 
-	method(#class) forMutualExclusion
-	{
-		| sem |
-		sem := self new.
-		sem signal.
-		^sem
-	}
-
 	## ==================================================================
 
 	method(#primitive) signal.
 	method(#primitive) wait.
 
-(*
-TODO: timed wait...
-	method waitWithTimeout: seconds
-	{
-		| s |
-		s := Semaphore new.
-		Processor signal: s after: seconds.
-		self waitWithTimedSemaphore: s.
-
-		if (self.
-	}
-
-	method waitWithTimeout: seconds and: nanoSeconds
-	{
-		<primitive: #_semaphore_wait>
-		self primitiveFailed
-	}
-*)
-
-	(* TODO: MIGRATE TO MUTEX...
-	method critical: aBlock
-	{
-		self wait.
-		^aBlock ensure: [ self signal ]
-	}*)
-
-	
 	## ==================================================================
 
 	method heapIndex
@@ -145,8 +110,14 @@ class Mutex(Semaphore)
 		^s.
 	}
 
-	method lock  { ^self wait }
-	method unlock { ^self signal }
+(*
+TODO: how to prohibit wait and signal???
+	method(#prohibited) wait.
+	method(#prohibited) signal.
+*)
+
+	method lock  { ^super wait }
+	method unlock { ^super signal }
 
 	method critical: block
 	{
diff --git a/moo/kernel/test-002.moo b/moo/kernel/test-002.moo
index a33fe24..2e3349d 100644
--- a/moo/kernel/test-002.moo
+++ b/moo/kernel/test-002.moo
@@ -49,6 +49,42 @@ class MyObject(Object)
 		^true
 	}
 
+	method(#class) test_mutex
+	{
+		| mtx sem v p q |
+
+		mtx := Mutex new.
+		sem := Semaphore new.
+
+		p := 0.
+
+		[ mtx lock.
+		  v := 0.
+		  2000 timesRepeat: [v := v + 1. p := p + 1. ].
+		  q := v.
+		  mtx unlock.
+		  sem signal.
+		] fork.
+
+		[ mtx critical: [
+		     v := 0.
+		     2000 timesRepeat: [v := v + 1. p := p + 1. ].
+		     q := v.
+		  ].
+		  sem signal.
+		] fork.
+
+		mtx lock.
+		v := 0.
+		2000 timesRepeat: [v := v + 1. p := p + 1. ].
+		mtx unlock.
+
+		sem wait.
+		sem wait.
+
+		^%( v, p ) ## v must be 2000, p must be 6000
+	}
+
 	method(#class) main
 	{
 		| tc limit |
@@ -57,7 +93,8 @@ class MyObject(Object)
 			## 0 - 4
 			[ self proc1 == 100 ], 
 			[ Processor sleepFor: 2.  self proc1 == 200 ],
-			[ self test_semaphore_heap == true ]
+			[ self test_semaphore_heap == true ],
+			[ self test_mutex = #(2000 6000) ]
 		).
 
 		limit := tc size.
diff --git a/moo/kernel/test-003.moo b/moo/kernel/test-003.moo
index 2fe42fa..db713a4 100644
--- a/moo/kernel/test-003.moo
+++ b/moo/kernel/test-003.moo
@@ -67,16 +67,19 @@ class MyObject(TestObject)
 			[(Apex isKindOf: Class) == true],
 			[(Apex isKindOf: Apex) == true],
 			[(SmallInteger isKindOf: Integer) == false],
-			[(10 isKindOf: Integer) == true],
-			[(10 isKindOf: 20) == false],
+			[(SmallInteger isKindOf: SmallInteger) == false],
+			[(Object isKindOf: SmallInteger) == false],
 
 			## 10-14
+			[(10 isKindOf: Integer) == true],
+			[(10 isKindOf: 20) == false],
 			[([] isKindOf: BlockContext) == true],
 			[([] isKindOf: MethodContext) == false],
 			[([] isKindOf: Context) == true],
+
+			## 15-20
 			[('string' isKindOf: String) == true],
 			[(#symbol isKindOf: String) == true],
-
 			[('string' isKindOf: Symbol) == false],
 			[(#symbol isKindOf: Symbol) == true]
 		).
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index f1ab703..adf4dde 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -494,8 +494,8 @@ static MOO_INLINE void chain_into_semaphore (moo_t* moo, moo_oop_process_t proc,
 	MOO_ASSERT (moo, (moo_oop_t)proc->sem_wait.next == moo->_nil);
 
 	/* a semaphore or a semaphore group must be given for process chaining */
-	MOO_ASSERT (moo, MOO_CLASSOF(moo,sem) == moo->_semaphore ||
-	                 MOO_CLASSOF(moo,sem) == moo->_semaphore_group);
+	MOO_ASSERT (moo, moo_iskindof(moo, (moo_oop_t)sem, moo->_semaphore) ||
+	                 moo_iskindof(moo, (moo_oop_t)sem, moo->_semaphore_group));
 
 	/* i assume the head part of the semaphore has the same layout as
 	 * the semaphore group */
@@ -513,8 +513,8 @@ static MOO_INLINE void unchain_from_semaphore (moo_t* moo, moo_oop_process_t pro
 
 	MOO_ASSERT (moo, (moo_oop_t)proc->sem != moo->_nil);
 
-	MOO_ASSERT (moo, MOO_CLASSOF(moo, proc->sem) == moo->_semaphore ||
-	                 MOO_CLASSOF(moo, proc->sem) == moo->_semaphore_group);
+	MOO_ASSERT (moo, moo_iskindof(moo, proc->sem, moo->_semaphore) ||
+	                 moo_iskindof(moo, proc->sem, moo->_semaphore_group));
 
 	MOO_ASSERT (moo, MOO_OFFSETOF(moo_semaphore_t,waiting) ==
 	                 MOO_OFFSETOF(moo_semaphore_group_t,waiting));
@@ -859,7 +859,7 @@ static MOO_INLINE moo_oop_t await_semaphore_group (moo_t* moo, moo_oop_semaphore
 	moo_oop_semaphore_t sem;
 	moo_ooi_t numsems, sempos, i, count;
 
-	MOO_ASSERT (moo, MOO_CLASSOF(moo,semgrp) == moo->_semaphore_group);
+	MOO_ASSERT (moo, moo_iskindof(moo, (moo_oop_t)semgrp, moo->_semaphore_group));
 
 	/* check if there is a signaled semaphore in the group */
 	numsems = MOO_OOP_TO_SMOOI(semgrp->size);
@@ -1673,15 +1673,10 @@ static moo_pfrc_t pf_not_identical (moo_t* moo, moo_ooi_t nargs)
 	return MOO_PF_SUCCESS;
 }
 
-static moo_pfrc_t _equal_objects (moo_t* moo, moo_ooi_t nargs)
+static int _equal_objects (moo_t* moo, moo_oop_t rcv, moo_oop_t arg)
 {
-	moo_oop_t rcv, arg;
 	int rtag;
 
-	MOO_ASSERT (moo, nargs == 1);
-
-	rcv = MOO_STACK_GETRCV(moo, nargs);
-	arg = MOO_STACK_GETARG(moo, nargs, 0);
 	if (rcv == arg) return 1; /* identical. so equal */
 
 	rtag = MOO_OOP_GET_TAG(rcv);
@@ -1721,18 +1716,33 @@ static moo_pfrc_t _equal_objects (moo_t* moo, moo_ooi_t nargs)
 				case MOO_OBJ_TYPE_CHAR:
 				case MOO_OBJ_TYPE_HALFWORD:
 				case MOO_OBJ_TYPE_WORD:
-					return (MOO_MEMCMP (((moo_oop_byte_t)rcv)->slot, ((moo_oop_byte_t)arg)->slot, MOO_BYTESOF(moo,rcv)) == 0)? 1: 0;
+					return (MOO_MEMCMP (MOO_OBJ_GET_BYTE_SLOT(rcv), MOO_OBJ_GET_BYTE_SLOT(arg), MOO_BYTESOF(moo,rcv)) == 0)? 1: 0;
 
 				default:
+				{
 					if (rcv == moo->_nil) return arg == moo->_nil? 1: 0;
 					if (rcv == moo->_true) return arg == moo->_true? 1: 0;
 					if (rcv == moo->_false) return arg == moo->_false? 1: 0;
-					
-					/* MOO_OBJ_TYPE_OOP, ... */
-					MOO_DEBUG1 (moo, "<_equal_objects> Cannot compare objects of type %d\n", (int)MOO_OBJ_GET_FLAGS_TYPE(rcv));
 
+					/* MOO_OBJ_TYPE_OOP, ... */
+					MOO_ASSERT (moo, MOO_OBJ_GET_FLAGS_TYPE(rcv) == MOO_OBJ_TYPE_OOP);
+
+				#if 1
+					MOO_DEBUG1 (moo, "<_equal_objects> Cannot compare objects of type %d\n", (int)MOO_OBJ_GET_FLAGS_TYPE(rcv));
 					moo_seterrnum (moo, MOO_ENOIMPL); /* TODO: better error code */
 					return -1;
+				#else
+					for (i = 0; i < MOO_OBJ_GET_SIZE(rcv); i++)
+					{
+						/* TODO: remove recursion */
+
+						/* NOTE: even if the object implements the equality method, 
+						 * this primitive method doesn't honor it. */
+						if (!_equal_objects(moo, ((moo_oop_oop_t)rcv)->slot[i], ((moo_oop_oop_t)arg)->slot[i])) return 0;
+					}
+					return 1;
+				#endif
+				}
 			}
 		}
 	}
@@ -1740,9 +1750,13 @@ static moo_pfrc_t _equal_objects (moo_t* moo, moo_ooi_t nargs)
 
 static moo_pfrc_t pf_equal (moo_t* moo, moo_ooi_t nargs)
 {
+	moo_oop_t rcv, arg;
 	int n;
 
-	n = _equal_objects (moo, nargs);
+	rcv = MOO_STACK_GETRCV(moo, nargs);
+	arg = MOO_STACK_GETARG(moo, nargs, 0);
+
+	n = _equal_objects (moo, rcv, arg);
 	if (n <= -1) return MOO_PF_FAILURE;
 
 	MOO_STACK_SETRET (moo, nargs, (n? moo->_true: moo->_false));
@@ -1751,9 +1765,13 @@ static moo_pfrc_t pf_equal (moo_t* moo, moo_ooi_t nargs)
 
 static moo_pfrc_t pf_not_equal (moo_t* moo, moo_ooi_t nargs)
 {
+	moo_oop_t rcv, arg;
 	int n;
 
-	n = _equal_objects (moo, nargs);
+	rcv = MOO_STACK_GETRCV(moo, nargs);
+	arg = MOO_STACK_GETARG(moo, nargs, 0);
+
+	n = _equal_objects (moo, rcv, arg);
 	if (n <= -1) return MOO_PF_FAILURE;
 
 	MOO_STACK_SETRET (moo, nargs, (n? moo->_false: moo->_true));
@@ -2588,7 +2606,7 @@ static moo_pfrc_t pf_processor_add_gcfin_semaphore (moo_t* moo, moo_ooi_t nargs)
 
 	MOO_ASSERT (moo, nargs == 1);
 	sem = (moo_oop_semaphore_t)MOO_STACK_GETARG(moo, nargs, 0);
-	MOO_PF_CHECK_ARGS (moo, nargs, MOO_CLASSOF(moo,sem) == moo->_semaphore);
+	MOO_PF_CHECK_ARGS (moo, nargs, moo_iskindof(moo, (moo_oop_t)sem, moo->_semaphore));
 
 /* TODO: no overwriting.. */
 	moo->sem_gcfin = sem;
diff --git a/moo/lib/moo-prv.h b/moo/lib/moo-prv.h
index f72dd59..776aec0 100644
--- a/moo/lib/moo-prv.h
+++ b/moo/lib/moo-prv.h
@@ -359,7 +359,7 @@ struct moo_iotok_t
 		MOO_IOTOK_RPAREN,
 		MOO_IOTOK_HASHPAREN,   /* #( - array literal */
 		MOO_IOTOK_HASHBRACK,   /* #[ - byte array literal */
-		MOO_IOTOK_PERCPAREN,   /* %{ - array expression */
+		MOO_IOTOK_PERCPAREN,   /* %( - array expression */
 		MOO_IOTOK_PERCBRACE,   /* %{ - dictionary expression */
 		MOO_IOTOK_PERIOD,
 		MOO_IOTOK_COMMA,