diff --git a/luprex/core/cpp/world-difftab.cpp b/luprex/core/cpp/world-difftab.cpp
index 112f57b0..08b217e2 100644
--- a/luprex/core/cpp/world-difftab.cpp
+++ b/luprex/core/cpp/world-difftab.cpp
@@ -166,11 +166,12 @@ static void transmit_value_debug_string(StreamBuffer *sb, std::ostringstream &os
     }
 }
 
-static bool diff_tables(lua_State *synch, lua_State *master, bool cmeta, StreamBuffer *sb) {
-    LuaArg mtnmap, mtab, stnmap, stab;
+static bool diff_tables(LuaStack &SLS0, LuaSlot stnmap, LuaSlot stab,
+                        LuaStack &MLS0, LuaSlot mtnmap, LuaSlot mtab,
+                        bool cmeta, StreamBuffer *sb) {
     LuaVar skey, mkey, sval, mval, mnil;
-    LuaStack SLS(synch, stnmap, stab, skey, sval);
-    LuaStack MLS(master, mtnmap, mtab, mkey, mval, mnil);
+    LuaStack SLS(SLS0.state(), skey, sval);
+    LuaStack MLS(MLS0.state(), mkey, mval, mnil);
     MLS.set(mnil, LuaNil);
     int nupdates = 0;
 
@@ -296,9 +297,9 @@ static void patch_table(LuaStack &LS0, LuaSlot tangibles, LuaSlot ntmap, LuaSlot
 
 void World::diff_numbered_tables(lua_State *master, StreamBuffer *sb) {
     lua_State *synch = state();
-    LuaVar sntmap, mntmap, stnmap, mtnmap;
-    LuaStack SLS(synch, sntmap, stnmap);
-    LuaStack MLS(master, mntmap, mtnmap);
+    LuaVar sntmap, mntmap, stnmap, mtnmap, stab, mtab;
+    LuaStack SLS(synch, sntmap, stnmap, stab);
+    LuaStack MLS(master, mntmap, mtnmap, mtab);
     SLS.rawget(sntmap, LuaRegistry, "ntmap");
     MLS.rawget(mntmap, LuaRegistry, "ntmap");
     SLS.rawget(stnmap, LuaRegistry, "tnmap");
@@ -313,23 +314,19 @@ void World::diff_numbered_tables(lua_State *master, StreamBuffer *sb) {
     int s_top = lua_gettop(synch);
     int m_top = lua_gettop(master);
     for (int id = 1; id <= m_ntables; id++) {
-        lua_pushvalue(master, mtnmap.index());
-        lua_rawgeti(master, mtnmap.index(), id);
-        if (lua_type(master, -1) == LUA_TTABLE) {
-            lua_pushvalue(synch, stnmap.index());
-            lua_rawgeti(synch, sntmap.index(), id);
+        MLS.rawgeti(mtab, mntmap, id);
+        if (MLS.istable(mtab)) {
+            SLS.rawgeti(stab, sntmap, id);
             int tw = sb->total_writes();
             sb->write_int32(id);
             nmodified += 1;
-            if (!diff_tables(synch, master, true, sb)) {
+            if (!diff_tables(SLS, stnmap, stab, MLS, mtnmap, mtab, true, sb)) {
                 sb->unwrite_to(tw);
                 nmodified -= 1;
             }
-            assert(lua_gettop(synch) == s_top);
-            assert(lua_gettop(master) == m_top);
-        } else {
-            lua_pop(master, 2);
         }
+        assert(lua_gettop(synch) == s_top);
+        assert(lua_gettop(master) == m_top);
     }
     sb->overwrite_int32(write_count_after, nmodified);
 }
@@ -337,9 +334,9 @@ void World::diff_numbered_tables(lua_State *master, StreamBuffer *sb) {
 
 void World::diff_tangible_databases(const IdVector &basis, lua_State *master, StreamBuffer *sb) {
     lua_State *synch = state();
-    LuaVar stnmap, mtnmap, stangibles, mtangibles;
-    LuaStack SLS(synch, stnmap, stangibles);
-    LuaStack MLS(master, mtnmap, mtangibles);
+    LuaVar stnmap, mtnmap, stangibles, mtangibles, stab, mtab;
+    LuaStack SLS(synch, stnmap, stangibles, stab);
+    LuaStack MLS(master, mtnmap, mtangibles, mtab);
     SLS.rawget(stnmap, LuaRegistry, "tnmap");
     MLS.rawget(mtnmap, LuaRegistry, "tnmap");
     SLS.rawget(stangibles, LuaRegistry, "tangibles");
@@ -351,14 +348,12 @@ void World::diff_tangible_databases(const IdVector &basis, lua_State *master, St
     int s_top = lua_gettop(synch);
     int m_top = lua_gettop(master);
     for (int64_t id : basis) {
-        lua_pushvalue(master, mtnmap.index());
-        lua_rawgeti(master, mtangibles.index(), id);
-        lua_pushvalue(synch, stnmap.index());
-        lua_rawgeti(synch, stangibles.index(), id);
+        MLS.rawgeti(mtab, mtangibles, id);
+        SLS.rawgeti(stab, stangibles, id);
         int tw = sb->total_writes();
         sb->write_int64(id);
         nmodified += 1;
-        if (!diff_tables(synch, master, false, sb)) {
+        if (!diff_tables(SLS, stnmap, stab, MLS, mtnmap, mtab, false, sb)) {
             sb->unwrite_to(tw);
             nmodified -= 1;
         }
@@ -369,77 +364,79 @@ void World::diff_tangible_databases(const IdVector &basis, lua_State *master, St
 }
 
 LuaDefine(table_diffcompare, "c") {
-    LuaArg mtnmap, mtab, stnmap, stab;
+    LuaArg mtnmap, mtab, mstnmap, mstab, stnmap, stab;
     LuaRet dbgstring;
     LuaVar tthread;
-    LuaStack LS(L, mtnmap, mtab, stnmap, stab, dbgstring, tthread);
+    LuaStack MLS(L, mtnmap, mtab, mstnmap, mstab, dbgstring, tthread);
     // Check the arguments.
-    LS.checktable(mtnmap);
-    LS.checktable(stnmap);
-    LS.checktable(mtab);
-    LS.checktable(stab);
+    MLS.checktable(mtnmap);
+    MLS.checktable(mstnmap);
+    MLS.checktable(mtab);
+    MLS.checktable(mstab);
+
     // Create a temporary thread to be the 'synch model'.  We'll use the
-    // existing thread as the 'master model'.
+    // existing thread as the 'master model'.  Move two tables to the synch thread.
     lua_State *synch = lua_newthread(L);
     lua_replace(L, tthread.index());
+    lua_pushvalue(L, mstnmap.index());
+    lua_pushvalue(L, mstab.index());
+    lua_xmove(L, synch, 2);
+    LuaStack SLS(synch, stnmap, stab);
+
     // Call tablecmp_diff.
     StreamBuffer sb;
-    lua_pushvalue(L, stnmap.index());
-    lua_pushvalue(L, stab.index());
-    lua_xmove(L, synch, 2);
-    lua_pushvalue(L, mtnmap.index());
-    lua_pushvalue(L, mtab.index());
-    diff_tables(synch, L, true, &sb);
+    diff_tables(SLS, stnmap, stab, MLS, mtnmap, mtab, true, &sb);
+
     // Convert the output to a debug string.
-    LS.set(dbgstring, diff_tables_debug_string(&sb));
-    return LS.result();
+    MLS.set(dbgstring, diff_tables_debug_string(&sb));
+    return MLS.result();
 }
 
 LuaDefine(table_diffapply, "c") {
-    LuaArg tnmap, mtab, stab;
+    LuaArg mtnmap, mtab, mstab, stnmap, stab;
     LuaRet eql, eqlstr, rtab;
-    LuaVar tthread, tangibles, ntmap, key, val;
-    LuaStack LS(L, tnmap, mtab, stab, eql, eqlstr, rtab, tthread, tangibles, ntmap, key, val);
+    LuaVar tthread, tangibles, mntmap, key, val;
+    LuaStack MLS(L, mtnmap, mtab, mstab, eql, eqlstr, rtab, tthread, tangibles, mntmap, key, val);
     // Check the arguments.
-    LS.checktable(tnmap);
-    LS.checktable(mtab);
-    LS.checktable(stab);
+    MLS.checktable(mtnmap);
+    MLS.checktable(mtab);
+    MLS.checktable(mstab);
 
     // Get the tangibles map.
-    LS.rawget(tangibles, LuaRegistry, "tangibles");
+    MLS.rawget(tangibles, LuaRegistry, "tangibles");
 
     // Invert the tnmap to make the ntmap.
-    LS.set(ntmap, LuaNewTable);
-    LS.set(key, LuaNil);
-    while (LS.next(tnmap, key, val)) {
-        LS.rawset(ntmap, val, key);
+    MLS.set(mntmap, LuaNewTable);
+    MLS.set(key, LuaNil);
+    while (MLS.next(mtnmap, key, val)) {
+        MLS.rawset(mntmap, val, key);
     }
 
     // Create a temporary thread to be the 'synch model'.  We'll use the
     // existing thread as the 'master model'.
     lua_State *synch = lua_newthread(L);
     lua_replace(L, tthread.index());
-    // Call tablecmp_diff.
-    StreamBuffer sb;
-    lua_pushvalue(L, tnmap.index());
-    lua_pushvalue(L, stab.index());
+    lua_pushvalue(L, mtnmap.index());
+    lua_pushvalue(L, mstab.index());
     lua_xmove(L, synch, 2);
-    lua_pushvalue(L, tnmap.index());
-    lua_pushvalue(L, mtab.index());
-    diff_tables(synch, L, true, &sb);
+    LuaStack SLS(synch, stnmap, stab);
 
-    patch_table(LS, tangibles, ntmap, stab, &sb);
+    // Call diff_tables and patch_tables
+    StreamBuffer sb;
+    diff_tables(SLS, stnmap, stab, MLS, mtnmap, mtab, true, &sb);
 
-    LS.call(eql, table_equal, stab, mtab);
-    bool e = LS.ckboolean(eql);
+    patch_table(MLS, tangibles, mntmap, mstab, &sb);
+
+    MLS.call(eql, table_equal, mstab, mtab);
+    bool e = MLS.ckboolean(eql);
     if (e) {
-        LS.set(eqlstr, "tables equal");
+        MLS.set(eqlstr, "tables equal");
     } else {
-        LS.set(eqlstr, "tables were supposed to be equal");
+        MLS.set(eqlstr, "tables were supposed to be equal");
     }
-    LS.set(rtab, stab);
+    MLS.set(rtab, stab);
 
-    return LS.result();
+    return MLS.result();
 }