diff --git a/src/lalr/GrammarGenerator.cpp b/src/lalr/GrammarGenerator.cpp
index 69256f6..9e64370 100644
--- a/src/lalr/GrammarGenerator.cpp
+++ b/src/lalr/GrammarGenerator.cpp
@@ -150,18 +150,19 @@ std::string GrammarGenerator::label_item( const GrammarItem& item ) const
 
     LALR_ASSERT( item.index() >= 0 && item.index() < int(lookaheads_.size()) );
     const GrammarSymbolSet& lookaheads = lookaheads_[item.index()].lookaheads();
-    if ( !lookaheads.empty() )
+    const char* delimiter = " {";
+    for ( int i = 0; i < int(symbols_.size()); ++i )
     {
-        const char* delimiter = " {";
-        for ( const GrammarSymbol* lookahead : lookaheads )
+        if ( lookaheads.contains(i) )
         {
-            LALR_ASSERT( lookahead );
+            const GrammarSymbol* symbol = symbols_[i].get();
+            LALR_ASSERT( symbol );
             label += delimiter;
             delimiter = ", ";
-            label += lookahead->lexeme();
+            label += symbol->lexeme();
         }
-        label += "}";
     }
+    label += "}";
 
     return label;
 }
@@ -255,7 +256,7 @@ GrammarTransition* GrammarGenerator::reduce_transition( const GrammarSymbol* sym
 */
 GrammarSymbolSet GrammarGenerator::spontaneous_lookaheads( const GrammarItem& item ) const
 {
-    GrammarSymbolSet lookaheads;
+    GrammarSymbolSet lookaheads(symbols_.size());
 
     const GrammarProduction* production = productions_[item.production()].get();
     LALR_ASSERT( production );
@@ -703,20 +704,21 @@ void GrammarGenerator::calculate_reachable_productions_for_symbol( const Grammar
 */
 void GrammarGenerator::generate_spontaneous_lookaheads()
 {
-    lookaheads_.clear();
+    const size_t symbols = symbols_.size();
+    lookaheads_.clear();        
     for ( const shared_ptr<GrammarState>& state : states_ )
     {
         for ( const GrammarItem& item : state->items() )
         {
             int index = int(lookaheads_.size());
             item.set_index( index );
-            lookaheads_.emplace_back( const_cast<GrammarItem*>(&item) );
+            lookaheads_.emplace_back( const_cast<GrammarItem*>(&item), symbols );
             ++index;
         }
     }
 
     {
-        GrammarSymbolSet lookaheads;
+        GrammarSymbolSet lookaheads{ symbols };
         lookaheads.insert( end_symbol_ );
         GrammarItem* start_item = start_state_->find_item( start_symbol_->productions().front(), 0 );
         LALR_ASSERT( start_item );
@@ -946,7 +948,7 @@ void GrammarGenerator::generate_reduce_transitions()
     {
         GrammarState* state = i->get();
         LALR_ASSERT( state );
-            
+
         for ( set<GrammarItem>::const_iterator item = state->items().begin(); item != state->items().end(); ++item )
         {
             const GrammarProduction* production = productions_[item->production()].get();
@@ -954,11 +956,14 @@ void GrammarGenerator::generate_reduce_transitions()
             if ( item->position() >= production->length() )
             {
                 const GrammarSymbolSet& lookaheads = lookaheads_[item->index()].lookaheads();
-                for ( vector<const GrammarSymbol*>::const_iterator j = lookaheads.begin(); j != lookaheads.end(); ++j )
+                for ( int index = 0; index < int(symbols_.size()); ++index )
                 {
-                    const GrammarSymbol* symbol = *j;
-                    LALR_ASSERT( symbol );
-                    generate_reduce_transition( state, symbol, production );
+                    if ( lookaheads.contains(index) )
+                    {
+                        const GrammarSymbol* symbol = symbols_[index].get();
+                        LALR_ASSERT( symbol );
+                        generate_reduce_transition( state, symbol, production );
+                    }
                 }
             }                
         }
diff --git a/src/lalr/GrammarLookahead.cpp b/src/lalr/GrammarLookahead.cpp
index 02113a8..500dd13 100644
--- a/src/lalr/GrammarLookahead.cpp
+++ b/src/lalr/GrammarLookahead.cpp
@@ -6,26 +6,24 @@
 #include "GrammarLookahead.hpp"
 #include "GrammarItem.hpp"
 #include "assert.hpp"
+#include <utility>
 
 using std::vector;
 using namespace lalr;
 
-GrammarLookahead::GrammarLookahead( GrammarItem* item )
+GrammarLookahead::GrammarLookahead( GrammarItem* item, size_t symbols )
 : item_( item )
 , propagate_to_()
-, lookaheads_{}
+, lookaheads_{ symbols }
 {
     LALR_ASSERT( item_ );
 }
 
 GrammarLookahead::GrammarLookahead( GrammarLookahead&& item )
-: item_( nullptr )
-, propagate_to_()
-, lookaheads_()
+: item_{ std::exchange(item.item_, nullptr) }
+, propagate_to_{ std::move(item.propagate_to_) }
+, lookaheads_{ std::move(item.lookaheads_) }
 {
-    std::swap( item_, item.item_ );
-    std::swap( propagate_to_, item.propagate_to_ );
-    std::swap( lookaheads_, item.lookaheads_ );
 }
 
 GrammarItem* GrammarLookahead::item() const
diff --git a/src/lalr/GrammarLookahead.hpp b/src/lalr/GrammarLookahead.hpp
index 89082c8..d67f3f2 100644
--- a/src/lalr/GrammarLookahead.hpp
+++ b/src/lalr/GrammarLookahead.hpp
@@ -15,7 +15,7 @@ class GrammarLookahead
     GrammarSymbolSet lookaheads_;
 
 public:
-    GrammarLookahead( GrammarItem* item );
+    GrammarLookahead( GrammarItem* item, size_t symbols );
     GrammarLookahead( GrammarLookahead&& item );
 
     GrammarItem* item() const;
diff --git a/src/lalr/GrammarSymbol.cpp b/src/lalr/GrammarSymbol.cpp
index 689cba8..52efc8d 100644
--- a/src/lalr/GrammarSymbol.cpp
+++ b/src/lalr/GrammarSymbol.cpp
@@ -25,8 +25,8 @@ GrammarSymbol::GrammarSymbol( const std::string& lexeme )
 , index_( -1 )
 , nullable_( false )
 , referenced_in_precedence_directive_( false )
-, first_()
-, follow_()
+, first_{0}
+, follow_{0}
 , productions_()
 {
 }
diff --git a/src/lalr/GrammarSymbolSet.cpp b/src/lalr/GrammarSymbolSet.cpp
index ac4992f..78d32bc 100644
--- a/src/lalr/GrammarSymbolSet.cpp
+++ b/src/lalr/GrammarSymbolSet.cpp
@@ -10,23 +10,19 @@
 using std::vector;
 using namespace lalr;
 
-GrammarSymbolSet::GrammarSymbolSet()
+GrammarSymbolSet::GrammarSymbolSet( size_t symbols )
 : set_()
-, symbols_()
 {
+    set_.resize( symbols / 8 );
 }
 
 GrammarSymbolSet::GrammarSymbolSet( GrammarSymbolSet&& set )
-: set_()
-, symbols_()
+: set_( std::move(set.set_) )
 {
-    std::swap( set_, set.set_ );
-    std::swap( symbols_, set.symbols_ );
 }
 
 GrammarSymbolSet::GrammarSymbolSet( const GrammarSymbolSet& set )
 : set_( set.set_ )
-, symbols_( set.symbols_ )
 {
 }
 
@@ -35,7 +31,6 @@ GrammarSymbolSet& GrammarSymbolSet::operator=( GrammarSymbolSet&& set )
     if ( this != &set )
     {
         std::swap( set_, set.set_ );
-        std::swap( symbols_, set.symbols_ );
     }
     return *this;
 }
@@ -45,34 +40,19 @@ GrammarSymbolSet& GrammarSymbolSet::operator=( const GrammarSymbolSet& set )
     if ( this != &set )
     {
         set_ = set.set_;
-        symbols_ = set.symbols_;
     }
     return *this;    
 }
 
-size_t GrammarSymbolSet::empty() const
+bool GrammarSymbolSet::contains( int symbol_index ) const
 {
-    return symbols_.empty();
-}
-
-size_t GrammarSymbolSet::size() const
-{
-    return symbols_.size();
-}
-
-std::vector<const GrammarSymbol*>::const_iterator GrammarSymbolSet::begin() const
-{
-    return symbols_.begin();
-}
-
-std::vector<const GrammarSymbol*>::const_iterator GrammarSymbolSet::end() const
-{
-    return symbols_.end();
-}
-
-const std::vector<const GrammarSymbol*>& GrammarSymbolSet::symbols() const
-{
-    return symbols_;
+    size_t index = symbol_index / 8;
+    if ( index < set_.size() )
+    {
+        unsigned char mask = 1 << (symbol_index % 8);
+        return (set_[index] & mask) != 0;
+    }
+    return false;
 }
 
 bool GrammarSymbolSet::insert( const GrammarSymbol* symbol )
@@ -88,7 +68,7 @@ bool GrammarSymbolSet::insert( const GrammarSymbol* symbol )
         if ( !(set_[index] & mask) )
         {
             set_[index] |= mask;
-            symbols_.push_back( symbol );
+            // symbols_.push_back( symbol );
             return true;
         }
     }
@@ -97,12 +77,21 @@ bool GrammarSymbolSet::insert( const GrammarSymbol* symbol )
 
 int GrammarSymbolSet::insert( const GrammarSymbolSet& set )
 {
-    int added = 0;
-    const vector<const GrammarSymbol*>& symbols = set.symbols_;
-    for ( const GrammarSymbol* symbol : symbols )
+    if ( set_.size() < set.set_.size() )
     {
-        LALR_ASSERT( symbol );
-        added += insert( symbol ) ? 1 : 0;
+        set_.insert( set_.end(), set.set_.size() - set_.size(), 0 );
+    }
+
+    int added = 0;
+    for ( size_t i = 0; i < set.set_.size(); ++i )
+    {
+        unsigned char mask = set_[i];
+        unsigned char new_mask = mask | set.set_[i];
+        if ( mask != new_mask )
+        {
+            set_[i] = new_mask;
+            ++added;
+        }
     }
     return added;
 }
@@ -110,5 +99,4 @@ int GrammarSymbolSet::insert( const GrammarSymbolSet& set )
 void GrammarSymbolSet::swap( GrammarSymbolSet&& set )
 {
     std::swap( set_, set.set_ );
-    std::swap( symbols_, set.symbols_ );
 }
diff --git a/src/lalr/GrammarSymbolSet.hpp b/src/lalr/GrammarSymbolSet.hpp
index 732a371..fd9444e 100644
--- a/src/lalr/GrammarSymbolSet.hpp
+++ b/src/lalr/GrammarSymbolSet.hpp
@@ -12,20 +12,15 @@ class GrammarSymbol;
 class GrammarSymbolSet
 {
     std::vector<unsigned char> set_;
-    std::vector<const GrammarSymbol*> symbols_;
 
 public:
-    GrammarSymbolSet();
+    GrammarSymbolSet( size_t symbols );
     GrammarSymbolSet( GrammarSymbolSet&& set );
     GrammarSymbolSet( const GrammarSymbolSet& set );
     GrammarSymbolSet& operator=( GrammarSymbolSet&& set );
     GrammarSymbolSet& operator=( const GrammarSymbolSet& set );
 
-    size_t empty() const;
-    size_t size() const;
-    std::vector<const GrammarSymbol*>::const_iterator begin() const;
-    std::vector<const GrammarSymbol*>::const_iterator end() const;
-    const std::vector<const GrammarSymbol*>& symbols() const;
+    bool contains( int symbol_index ) const;
     bool insert( const GrammarSymbol* symbol );
     int insert( const GrammarSymbolSet& set );
     void swap( GrammarSymbolSet&& set );