diff -ru lua/include/lua.h lua-4.0-bool/include/lua.h
--- lua/include/lua.h	Tue Oct 31 13:44:07 2000
+++ lua-4.0-bool/include/lua.h	Fri Sep 21 00:35:33 2001
@@ -32,7 +32,8 @@
 
 
 /* pre-defined references */
-#define LUA_NOREF	(-2)
+#define LUA_NOREF	(-3)
+#define LUA_REFFALSE	(-2)
 #define LUA_REFNIL	(-1)
 #define LUA_REFREGISTRY	0
 
@@ -68,10 +69,11 @@
 
 #define LUA_TUSERDATA	0
 #define LUA_TNIL	1
-#define LUA_TNUMBER	2
-#define LUA_TSTRING	3
-#define LUA_TTABLE	4
-#define LUA_TFUNCTION	5
+#define LUA_TFALSE	2
+#define LUA_TNUMBER	3
+#define LUA_TSTRING	4
+#define LUA_TTABLE	5
+#define LUA_TFUNCTION	6
 
 
 
@@ -102,6 +104,7 @@
 LUA_API int            lua_isnumber (lua_State *L, int index);
 LUA_API int            lua_isstring (lua_State *L, int index);
 LUA_API int            lua_iscfunction (lua_State *L, int index);
+LUA_API int            lua_istrue (lua_State *L, int index);
 LUA_API int            lua_tag (lua_State *L, int index);
 
 LUA_API int            lua_equal (lua_State *L, int index1, int index2);
@@ -119,6 +122,7 @@
 ** push functions (C -> stack)
 */
 LUA_API void  lua_pushnil (lua_State *L);
+LUA_API void  lua_pushfalse (lua_State *L);
 LUA_API void  lua_pushnumber (lua_State *L, double n);
 LUA_API void  lua_pushlstring (lua_State *L, const char *s, size_t len);
 LUA_API void  lua_pushstring (lua_State *L, const char *s);
@@ -203,6 +207,7 @@
 #define lua_istable(L,n)	(lua_type(L,n) == LUA_TTABLE)
 #define lua_isuserdata(L,n)	(lua_type(L,n) == LUA_TUSERDATA)
 #define lua_isnil(L,n)		(lua_type(L,n) == LUA_TNIL)
+#define lua_isfalse(L,n)	(lua_type(L,n) == LUA_TFALSE)
 #define lua_isnull(L,n)		(lua_type(L,n) == LUA_TNONE)
 
 #define lua_getregistry(L)	lua_getref(L, LUA_REFREGISTRY)
diff -ru lua/src/lapi.c lua-4.0-bool/src/lapi.c
--- lua/src/lapi.c	Mon Oct 30 13:50:09 2000
+++ lua-4.0-bool/src/lapi.c	Fri Sep 21 00:36:24 2001
@@ -122,6 +122,11 @@
   return (o == NULL) ? 0 : iscfunction(o);
 }
 
+LUA_API int lua_istrue (lua_State *L, int index) {
+  StkId o = luaA_indexAcceptable(L, index);
+  return (o == NULL) ? 0 : istrue(o);
+}
+
 LUA_API int lua_isnumber (lua_State *L, int index) {
   TObject *o = luaA_indexAcceptable(L, index);
   return (o == NULL) ? 0 : (tonumber(o) == 0);
@@ -205,6 +210,12 @@
 }
 
 
+LUA_API void lua_pushfalse (lua_State *L) {
+  ttype(L->top) = LUA_TFALSE;
+  api_incr_top(L);
+}
+
+
 LUA_API void lua_pushnumber (lua_State *L, double n) {
   nvalue(L->top) = n;
   ttype(L->top) = LUA_TNUMBER;
@@ -289,6 +300,8 @@
 LUA_API int lua_getref (lua_State *L, int ref) {
   if (ref == LUA_REFNIL)
     ttype(L->top) = LUA_TNIL;
+  else if (ref == LUA_REFFALSE)
+    ttype(L->top) = LUA_TFALSE;
   else if (0 <= ref && ref < L->refSize &&
           (L->refArray[ref].st == LOCK || L->refArray[ref].st == HOLD))
     *L->top = L->refArray[ref].o;
@@ -354,6 +367,8 @@
   int ref;
   if (ttype(L->top-1) == LUA_TNIL)
     ref = LUA_REFNIL;
+  else if (ttype(L->top-1) == LUA_TFALSE)
+    ref = LUA_REFFALSE;
   else {
     if (L->refFree != NONEXT) {  /* is there a free place? */
       ref = L->refFree;
diff -ru lua/src/lcode.c lua-4.0-bool/src/lcode.c
--- lua/src/lcode.c	Fri Sep 29 14:42:13 2000
+++ lua-4.0-bool/src/lcode.c	Fri Sep 21 00:22:20 2001
@@ -321,7 +321,7 @@
     else {  /* expression has jumps */
       int final;  /* position after whole expression */
       int j = NO_JUMP;  /*  eventual  jump over values */
-      int p_nil = NO_JUMP;  /* position of an eventual PUSHNIL */
+      int p_nil = NO_JUMP;  /* position of an eventual PUSHFALSE */
       int p_1 = NO_JUMP;  /* position of an eventual PUSHINT */
       if (ISJUMP(previous) || need_value(fs, v->u.l.f, OP_JMPONF)
                            || need_value(fs, v->u.l.t, OP_JMPONT)) {
@@ -333,7 +333,7 @@
           /* correct stack for compiler and symbolic execution */
           luaK_adjuststack(fs, 1);
         }
-        p_nil = code_label(fs, OP_PUSHNILJMP, 0);
+        p_nil = code_label(fs, OP_PUSHFALSESKIP, 0);
         p_1 = code_label(fs, OP_PUSHINT, 1);
         luaK_patchlist(fs, j, luaK_getlabel(fs));
       }
@@ -548,6 +548,12 @@
       }
       break;
     }
+#if 0
+    /* ET:
+    ** These optimizations do not work with two _different_ false values.
+    ** "if x~=nil" is not the same as "if x"
+    ** "if x==nil" is not the same as "if not x"
+    */
     case OP_JMPNE: {
       if (i == CREATE_U(OP_PUSHNIL, 1)) {  /* `a~=nil' */
         i = CREATE_S(OP_JMPT, NO_JUMP);
@@ -563,6 +569,7 @@
       }
       break;
     }
+#endif
     case OP_JMPT:
     case OP_JMPONT: {
       switch (GET_OPCODE(i)) {
@@ -578,8 +585,9 @@
           }
           break;
         }
+	case OP_PUSHFALSE:
         case OP_PUSHNIL: {
-          if (GETARG_U(i) == 1) {
+          if (i == CREATE_0(OP_PUSHFALSE) || GETARG_U(i) == 1) {
             fs->pc--;  /* erase previous instruction */
             luaK_deltastack(fs, -1);  /* correct stack */
             return NO_JUMP; 
@@ -603,8 +611,10 @@
           luaK_deltastack(fs, -1);  /* correct stack */
           return NO_JUMP; 
         }
+	case OP_PUSHFALSE:
         case OP_PUSHNIL: {  /* `repeat ... until nil' */
-          if (GETARG_U(i) == 1) {
+	  if (o == OP_JMPF) /*ET: JMPONF must keep the nil/false value */
+          if (i == CREATE_0(OP_PUSHFALSE) || GETARG_U(i) == 1) {
             i = CREATE_S(OP_JMP, NO_JUMP);
             optm = 1;
           }
@@ -652,6 +662,7 @@
   {iU, 0, 0},	/* OP_RETURN */
   {iAB, 0, 0},	/* OP_CALL */
   {iAB, 0, 0},	/* OP_TAILCALL */
+  {iO, 1, 0},	/* OP_PUSHFALSE */
   {iU, VD, 0},	/* OP_PUSHNIL */
   {iU, VD, 0},	/* OP_POP */
   {iS, 1, 0},	/* OP_PUSHINT */
@@ -691,7 +702,7 @@
   {iS, 0, 1},	/* OP_JMPONT */
   {iS, 0, 1},	/* OP_JMPONF */
   {iS, 0, 0},	/* OP_JMP */
-  {iO, 0, 0},	/* OP_PUSHNILJMP */
+  {iO, 0, 0},	/* OP_PUSHFALSESKIP */
   {iS, 0, 0},	/* OP_FORPREP */
   {iS, 0, 3},	/* OP_FORLOOP */
   {iS, 2, 0},	/* OP_LFORPREP */
diff -ru lua/src/lib/lbaselib.c lua-4.0-bool/src/lib/lbaselib.c
--- lua/src/lib/lbaselib.c	Mon Nov  6 14:45:18 2000
+++ lua-4.0-bool/src/lib/lbaselib.c	Fri Sep 21 00:37:30 2001
@@ -326,6 +326,9 @@
     case LUA_TUSERDATA:
       sprintf(buff, "userdata(%d): %p", lua_tag(L, 1), lua_touserdata(L, 1));
       break;
+    case LUA_TFALSE:
+      lua_pushstring(L, "false");
+      return 1;
     case LUA_TNIL:
       lua_pushstring(L, "nil");
       return 1;
@@ -375,7 +378,7 @@
 
 static int luaB_assert (lua_State *L) {
   luaL_checkany(L, 1);
-  if (lua_isnil(L, 1))
+  if (!lua_istrue(L, 1))
     luaL_verror(L, "assertion failed!  %.90s", luaL_opt_string(L, 2, ""));
   return 0;
 }
@@ -453,7 +456,7 @@
     lua_pushvalue(L, a-1);  /* -1 to compensate function */
     lua_pushvalue(L, b-2);  /* -2 to compensate function and `a' */
     lua_rawcall(L, 2, 1);
-    res = !lua_isnil(L, -1);
+    res = lua_istrue(L, -1);
     lua_pop(L, 1);
     return res;
   }
diff -ru lua/src/llex.c lua-4.0-bool/src/llex.c
--- lua/src/llex.c	Fri Oct 20 18:39:03 2000
+++ lua-4.0-bool/src/llex.c	Thu Sep 20 22:04:36 2001
@@ -29,7 +29,7 @@
 
 /* ORDER RESERVED */
 static const char *const token2string [] = {
-    "and", "break", "do", "else", "elseif", "end", "for",
+    "and", "break", "do", "else", "elseif", "end", "false", "for",
     "function", "if", "local", "nil", "not", "or", "repeat", "return", "then",
     "until", "while", "", "..", "...", "==", ">=", "<=", "~=", "", "", "<eof>"};
 
diff -ru lua/src/llex.h lua-4.0-bool/src/llex.h
--- lua/src/llex.h	Wed Sep 27 19:41:58 2000
+++ lua-4.0-bool/src/llex.h	Thu Sep 20 22:05:24 2001
@@ -23,8 +23,8 @@
 */
 enum RESERVED {
   /* terminal symbols denoted by reserved words */
-  TK_AND = FIRST_RESERVED, TK_BREAK,
-  TK_DO, TK_ELSE, TK_ELSEIF, TK_END, TK_FOR, TK_FUNCTION, TK_IF, TK_LOCAL,
+  TK_AND = FIRST_RESERVED, TK_BREAK, TK_DO,
+  TK_ELSE, TK_ELSEIF, TK_END, TK_FALSE, TK_FOR, TK_FUNCTION, TK_IF, TK_LOCAL,
   TK_NIL, TK_NOT, TK_OR, TK_REPEAT, TK_RETURN, TK_THEN, TK_UNTIL, TK_WHILE,
   /* other terminal symbols */
   TK_NAME, TK_CONCAT, TK_DOTS, TK_EQ, TK_GE, TK_LE, TK_NE, TK_NUMBER,
diff -ru lua/src/lobject.c lua-4.0-bool/src/lobject.c
--- lua/src/lobject.c	Fri Oct 20 18:36:32 2000
+++ lua-4.0-bool/src/lobject.c	Thu Sep 20 22:03:57 2001
@@ -21,8 +21,8 @@
 const TObject luaO_nilobject = {LUA_TNIL, {NULL}};
 
 
-const char *const luaO_typenames[] = {
-  "userdata", "nil", "number", "string", "table", "function"
+const char *const luaO_typenames[] = { /* ORDER LUA_T */
+  "userdata", "nil", "false", "number", "string", "table", "function"
 };
 
 
@@ -49,8 +49,8 @@
     case LUA_TFUNCTION:
       return clvalue(t1) == clvalue(t2);
     default:
-      LUA_ASSERT(ttype(t1) == LUA_TNIL, "invalid type");
-      return 1; /* LUA_TNIL */
+      LUA_ASSERT(ttype(t1) == LUA_TNIL || ttype(t1) == LUA_TFALSE, "invalid type");
+      return 1; /* LUA_TNIL, LUA_TFALSE */
   }
 }
 
diff -ru lua/src/lobject.h lua-4.0-bool/src/lobject.h
--- lua/src/lobject.h	Mon Oct 30 18:49:19 2000
+++ lua-4.0-bool/src/lobject.h	Thu Sep 20 21:56:49 2001
@@ -32,11 +32,11 @@
 
 
 /* mark for closures active in the stack */
-#define LUA_TMARK	6
+#define LUA_TMARK	7
 
 
 /* tags for values visible from Lua == first user-created tag */
-#define NUM_TAGS	6
+#define NUM_TAGS	7
 
 
 /* check whether `t' is a mark */
@@ -148,6 +148,7 @@
 
 
 #define iscfunction(o)	(ttype(o) == LUA_TFUNCTION && clvalue(o)->isC)
+#define istrue(o)	(ttype(o) != LUA_TNIL && ttype(o) != LUA_TFALSE)
 
 
 typedef struct Node {
diff -ru lua/src/lopcodes.h lua-4.0-bool/src/lopcodes.h
--- lua/src/lopcodes.h	Tue Oct 24 18:05:59 2000
+++ lua-4.0-bool/src/lopcodes.h	Fri Sep 21 00:26:42 2001
@@ -76,6 +76,7 @@
 ** J = S argument used as jump offset (relative to pc of next instruction)
 ** L = unsigned argument used as index of local variable
 ** N = U argument used as index to `knum'
+** (Note: comparisons to nil (true/false tests) handle false too.)
 */
 
 typedef enum {
@@ -88,6 +89,7 @@
 OP_CALL,/*	A B	v_n-v_1 f(at a)	r_b-r_1		f(v1,...,v_n)	*/
 OP_TAILCALL,/*	A B	v_n-v_1 f(at a)	(return)	f(v1,...,v_n)	*/
 
+OP_PUSHFALSE,/*	-	-		false				*/
 OP_PUSHNIL,/*	U	-		nil_1-nil_u			*/
 OP_POP,/*	U	a_u-a_1		-				*/
 
@@ -123,7 +125,7 @@
 OP_POW,/*	-	y x		x^y				*/
 OP_CONCAT,/*	U	v_u-v_1		v1..-..v_u			*/
 OP_MINUS,/*	-	x		-x				*/
-OP_NOT,/*	-	x		(x==nil)? 1 : nil		*/
+OP_NOT,/*	-	x		(x==nil)? 1 : false		*/
 
 OP_JMPNE,/*	J	y x		-		(x~=y)? PC+=s	*/
 OP_JMPEQ,/*	J	y x		-		(x==y)? PC+=s	*/
@@ -138,7 +140,7 @@
 OP_JMPONF,/*	J	x		(x==nil)? x : -	(x==nil)? PC+=s	*/
 OP_JMP,/*	J	-		-		PC+=s		*/
 
-OP_PUSHNILJMP,/* -	-		nil		PC++;		*/
+OP_PUSHFALSESKIP,/* -	-		false		PC++;		*/
 
 OP_FORPREP,/*	J							*/
 OP_FORLOOP,/*	J							*/
diff -ru lua/src/lparser.c lua-4.0-bool/src/lparser.c
--- lua/src/lparser.c	Fri Oct 27 13:39:52 2000
+++ lua-4.0-bool/src/lparser.c	Thu Sep 20 22:07:24 2001
@@ -623,6 +623,11 @@
       next(ls);
       break;
     }
+    case TK_FALSE: {  /* simpleexp -> FALSE */
+      luaK_code0(fs, OP_PUSHFALSE);
+      next(ls);
+      break;
+    }
     case '{': {  /* simpleexp -> constructor */
       constructor(ls);
       break;
diff -ru lua/src/ltable.c lua-4.0-bool/src/ltable.c
--- lua/src/ltable.c	Thu Oct 26 14:47:05 2000
+++ lua-4.0-bool/src/ltable.c	Thu Sep 20 21:49:34 2001
@@ -57,6 +57,9 @@
     case LUA_TFUNCTION:
       h = IntPoint(clvalue(key));
       break;
+    case LUA_TFALSE:
+      h = 0;
+      break;
     default:
       return NULL;  /* invalid key */
   }
@@ -138,9 +141,9 @@
 ** hash, change `key' for a number with the same hash.
 */
 void luaH_remove (Hash *t, TObject *key) {
-  if (ttype(key) == LUA_TNUMBER ||
+  if (ttype(key) == LUA_TNUMBER || ttype(key) == LUA_TFALSE ||
        (ttype(key) == LUA_TSTRING && tsvalue(key)->len <= 30))
-  return;  /* do not remove numbers nor small strings */
+  return;  /* do not remove false, numbers, or small strings */
   else {
     /* try to find a number `n' with the same hash as `key' */
     Node *mp = luaH_mainposition(t, key);
diff -ru lua/src/ltests.c lua-4.0-bool/src/ltests.c
--- lua/src/ltests.c	Tue Oct 31 14:10:24 2000
+++ lua-4.0-bool/src/ltests.c	Fri Sep 21 00:37:59 2001
@@ -417,6 +417,9 @@
     else if EQ("isnil") {
       lua_pushnumber(L, lua_isnil(L, getnum));
     }
+    else if EQ("istrue") {
+      lua_pushnumber(L, lua_istrue(L, getnum));
+    }
     else if EQ("isnull") {
       lua_pushnumber(L, lua_isnull(L, getnum));
     }
diff -ru lua/src/ltm.c lua-4.0-bool/src/ltm.c
--- lua/src/ltm.c	Tue Oct 31 14:10:24 2000
+++ lua-4.0-bool/src/ltm.c	Thu Sep 20 22:02:50 2001
@@ -54,6 +54,7 @@
 static const char luaT_validevents[NUM_TAGS][TM_N] = {
   {1, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1},  /* LUA_TUSERDATA */
   {1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1},  /* LUA_TNIL */
+  {1, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1},  /* LUA_TFALSE */
   {1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1},  /* LUA_TNUMBER */
   {1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1},  /* LUA_TSTRING */
   {0, 0, 1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 1},  /* LUA_TTABLE */
diff -ru lua/src/luac/print.h lua-4.0-bool/src/luac/print.h
--- lua/src/luac/print.h	Mon Nov  6 21:03:12 2000
+++ lua-4.0-bool/src/luac/print.h	Thu Sep 20 22:29:58 2001
@@ -8,6 +8,7 @@
   case OP_RETURN: P_OP("RETURN"); P_U; break;
   case OP_CALL: P_OP("CALL"); P_AB; break;
   case OP_TAILCALL: P_OP("TAILCALL"); P_AB; break;
+  case OP_PUSHFALSE: P_OP("PUSHFALSE"); P_NONE; break;
   case OP_PUSHNIL: P_OP("PUSHNIL"); P_U; break;
   case OP_POP: P_OP("POP"); P_U; break;
   case OP_PUSHINT: P_OP("PUSHINT"); P_S; break;
@@ -47,7 +48,7 @@
   case OP_JMPONT: P_OP("JMPONT"); P_J; break;
   case OP_JMPONF: P_OP("JMPONF"); P_J; break;
   case OP_JMP: P_OP("JMP"); P_J; break;
-  case OP_PUSHNILJMP: P_OP("PUSHNILJMP"); P_NONE; break;
+  case OP_PUSHFALSESKIP: P_OP("PUSHFALSESKIP"); P_NONE; break;
   case OP_FORPREP: P_OP("FORPREP"); P_J; break;
   case OP_FORLOOP: P_OP("FORLOOP"); P_J; break;
   case OP_LFORPREP: P_OP("LFORPREP"); P_J; break;
diff -ru lua/src/lvm.c lua-4.0-bool/src/lvm.c
--- lua/src/lvm.c	Thu Oct 26 14:47:05 2000
+++ lua-4.0-bool/src/lvm.c	Thu Sep 20 22:57:16 2001
@@ -281,7 +281,7 @@
     if (!call_binTM(L, top, TM_LT))
       luaG_ordererror(L, top-2);
     L->top--;
-    return (ttype(L->top) != LUA_TNIL);
+    return istrue(L->top);
   }
 }
 
@@ -388,6 +388,10 @@
         luaD_call(L, base+GETARG_A(i), LUA_MULTRET);
         return base+GETARG_B(i);
       }
+      case OP_PUSHFALSE: {
+	ttype(top++) = LUA_TFALSE;
+	break;
+      }
       case OP_PUSHNIL: {
         int n = GETARG_U(i);
         LUA_ASSERT(n>0, "invalid argument");
@@ -578,8 +582,7 @@
         break;
       }
       case OP_NOT: {
-        ttype(top-1) =
-           (ttype(top-1) == LUA_TNIL) ? LUA_TNUMBER : LUA_TNIL;
+        ttype(top-1) = istrue(top - 1) ? LUA_TFALSE : LUA_TNUMBER;
         nvalue(top-1) = 1;
         break;
       }
@@ -614,20 +617,22 @@
         break;
       }
       case OP_JMPT: {
-        if (ttype(--top) != LUA_TNIL) dojump(pc, i);
+	--top;
+	if (istrue(top)) dojump(pc, i);
         break;
       }
       case OP_JMPF: {
-        if (ttype(--top) == LUA_TNIL) dojump(pc, i);
+	--top;
+	if (!istrue(top)) dojump(pc, i);
         break;
       }
       case OP_JMPONT: {
-        if (ttype(top-1) == LUA_TNIL) top--;
+        if (!istrue(top-1)) top--;
         else dojump(pc, i);
         break;
       }
       case OP_JMPONF: {
-        if (ttype(top-1) != LUA_TNIL) top--;
+        if (istrue(top-1)) top--;
         else dojump(pc, i);
         break;
       }
@@ -635,8 +640,8 @@
         dojump(pc, i);
         break;
       }
-      case OP_PUSHNILJMP: {
-        ttype(top++) = LUA_TNIL;
+      case OP_PUSHFALSESKIP: {
+        ttype(top++) = LUA_TFALSE;
         pc++;
         break;
       }