diff --git a/src/bitboard.cpp b/src/bitboard.cpp
index 0829b536..b00a0488 100644
--- a/src/bitboard.cpp
+++ b/src/bitboard.cpp
@@ -24,9 +24,6 @@ uint8_t PopCnt16[1 << 16];
 
 Bitboard SquareBB[SQ_32];
 
-Bitboard StarSquareBB9;
-Bitboard StarSquareBB12;
-
 
 /// Bitboards::pretty() returns an ASCII representation of a bitboard suitable
 /// to be printed to standard output. Useful for debugging.
@@ -57,7 +54,4 @@ void Bitboards::init()
 
     for (Square s = SQ_BEGIN; s < SQ_END; ++s)
         SquareBB[s] = (1UL << s);
-
-    StarSquareBB9 = S4(16, 18, 20,  22);
-    StarSquareBB12 = S4(17, 19, 21, 23);
 }
diff --git a/src/bitboard.h b/src/bitboard.h
index a0eaa88b..8f2e989b 100644
--- a/src/bitboard.h
+++ b/src/bitboard.h
@@ -69,15 +69,6 @@ inline Bitboard square_bb(Square s) noexcept
     return SquareBB[s];
 }
 
-inline Bitboard star_square_bb_9() noexcept
-{
-    return StarSquareBB9;
-}
-
-inline Bitboard star_square_bb_12() noexcept
-{
-    return StarSquareBB12;
-}
 
 /// Overloads of bitwise operators between a Bitboard and a Square for testing
 /// whether a given bit is set in a bitboard, and for setting and clearing bits.
diff --git a/src/mills.cpp b/src/mills.cpp
index add3418e..477518b8 100644
--- a/src/mills.cpp
+++ b/src/mills.cpp
@@ -16,6 +16,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <cstring>
 #include <random>
 
 #include "bitboard.h"
diff --git a/src/movegen.cpp b/src/movegen.cpp
index 05f13e5e..dc80400f 100644
--- a/src/movegen.cpp
+++ b/src/movegen.cpp
@@ -16,16 +16,8 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <cassert>
-#include <random>
-#include <array>
-#include <cstring>
-
 #include "movegen.h"
 #include "position.h"
-#include "misc.h"
-#include "bitboard.h"
-#include "option.h"
 #include "mills.h"
 
 /// generate<PLACE> generates all places.
@@ -44,7 +36,7 @@ ExtMove *generate<PLACE>(Position &pos, ExtMove *moveList)
     return cur;
 }
 
-/// generate<PLACE> generates all places.
+/// generate<MOVE> generates all moves.
 /// Returns a pointer to the end of the move moves.
 template<>
 ExtMove *generate<MOVE>(Position &pos, ExtMove *moveList)
@@ -81,7 +73,7 @@ ExtMove *generate<MOVE>(Position &pos, ExtMove *moveList)
     return cur;
 }
 
-/// generate<PLACE> generates all removes.
+/// generate<REMOVE> generates all removes.
 /// Returns a pointer to the end of the move moves.
 template<>
 ExtMove *generate<REMOVE>(Position &pos, ExtMove *moveList)
@@ -145,7 +137,7 @@ ExtMove *generate<LEGAL>(Position &pos, ExtMove *moveList)
 
     default:
 #ifdef FLUTTER_UI
-        LOGD("generate(): action = %d\n", pos.get_action());
+        LOGD("generate(): action = %hu\n", pos.get_action());
 #endif
         assert(0);
         break;
diff --git a/src/movepick.cpp b/src/movepick.cpp
index b1284062..d2934ff1 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -16,8 +16,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <cassert>
-
 #include "movepick.h"
 
 // partial_insertion_sort() sorts moves in descending order up to and including
@@ -34,11 +32,7 @@ void partial_insertion_sort(ExtMove *begin, const ExtMove *end, int limit)
         }
 }
 
-/// Constructors of the MovePicker class. As arguments we pass information
-/// to help it to return the (presumably) good moves first, to decide which
-/// moves to return (in the quiescence search, for instance, we only want to
-/// search captures, promotions, and some checks) and how important good move
-/// ordering is at the current node.
+/// Constructors of the MovePicker class.
 
 /// MovePicker constructor for the main search
 MovePicker::MovePicker(Position &p) noexcept
diff --git a/src/position.cpp b/src/position.cpp
index 8df68514..44118dda 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -16,23 +16,12 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
-#include <cassert>
-#include <cstddef> // For offsetof()
-#include <cstring> // For std::memset, std::memcmp
 #include <iomanip>
 #include <sstream>
 
 #include "bitboard.h"
-#include "misc.h"
-#include "movegen.h"
 #include "position.h"
 #include "thread.h"
-#include "tt.h"
-#include "uci.h"
-
-#include "option.h"
-#include "rule.h"
 #include "mills.h"
 
 using std::string;
diff --git a/src/rule.cpp b/src/rule.cpp
index 4b44a985..e79e12c1 100644
--- a/src/rule.cpp
+++ b/src/rule.cpp
@@ -19,7 +19,6 @@
 #include <cstring>
 
 #include "rule.h"
-#include "types.h"
 
 struct Rule rule = {
         "打三棋(12连棋)",           // 打三棋
diff --git a/src/search.cpp b/src/search.cpp
index bba1ed85..94e63d6d 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -16,29 +16,13 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
-#include <cassert>
-#include <cmath>
-#include <cstring>   // For std::memset
-#include <iostream>
-#include <sstream>
-
 #include "evaluate.h"
-#include "misc.h"
-#include "movegen.h"
-#include "movepick.h"
-#include "position.h"
-#include "search.h"
 #include "thread.h"
-#include "tt.h"
-#include "uci.h"
+//#include "uci.h"
 
 #include "endgame.h"
-#include "types.h"
 #include "option.h"
 
-#include <random>
-
 using std::string;
 using Eval::evaluate;
 using namespace Search;
@@ -49,7 +33,7 @@ Value search(Position *pos, Sanmill::Stack<Position> &ss, Depth depth, Depth ori
 
 bool is_timeout(TimePoint startTime);
 
-/// Search::init() is called at startup to initialize various lookup tables
+/// Search::init() is called at startup
 
 void Search::init() noexcept
 {
@@ -437,7 +421,7 @@ Value search(Position *pos, Sanmill::Stack<Position> &ss, Depth depth, Depth ori
         // Check for a new best move
         // Finished searching the move. If a stop occurred, the return value of
         // the search cannot be trusted, and we return immediately without
-        // updating best move, PV and TT.
+        // updating best move and TT.
         if (Threads.stop.load(std::memory_order_relaxed))
             return VALUE_ZERO;
 
diff --git a/src/search.h b/src/search.h
index 94f320e4..9b84fe93 100644
--- a/src/search.h
+++ b/src/search.h
@@ -21,11 +21,7 @@
 
 #include <vector>
 
-#include "stack.h"
-#include "tt.h"
 #include "endgame.h"
-#include "movepick.h"
-#include "types.h"
 
 #ifdef CYCLE_STAT
 #include "stopwatch.h"
diff --git a/src/stack.h b/src/stack.h
index c0c2d556..eb80d68c 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -19,9 +19,6 @@
 #ifndef STACK_H
 #define STACK_H
 
-#include <cstdlib>
-#include <cassert>
-
 namespace Sanmill
 {
 
diff --git a/src/thread.cpp b/src/thread.cpp
index 6fa18f18..6b697fc3 100644
--- a/src/thread.cpp
+++ b/src/thread.cpp
@@ -16,15 +16,10 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <cassert>
-
-#include <algorithm> // For std::count
 #include <iomanip>
-#include "movegen.h"
-#include "search.h"
+
 #include "thread.h"
 #include "uci.h"
-#include "tt.h"
 #include "option.h"
 #include "mills.h"
 
@@ -84,7 +79,7 @@ Thread::~Thread()
 
 void Thread::clear() noexcept
 {
-    // TODO: Do nothing
+    // TODO: Reset histories
     return;
 }
 
@@ -549,11 +544,7 @@ void ThreadPool::start_thinking(Position *pos, bool ponderMode)
     increaseDepth = true;
     main()->ponder = ponderMode;
 
-    // We use Position::set() to set root position across threads. But there are
-    // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
-    // be deduced from a fen string, so set() clears them and they are set from
-    // setupStates->back() later. The rootState is per thread, earlier states are shared
-    // since they are read-only.
+    // We use Position::set() to set root position across threads.
     for (Thread *th : *this) {
         th->rootPos = pos;
     }
diff --git a/src/tt.cpp b/src/tt.cpp
index edbed2bc..e6d46027 100644
--- a/src/tt.cpp
+++ b/src/tt.cpp
@@ -20,7 +20,7 @@
 
 #ifdef TRANSPOSITION_TABLE_ENABLE
 
-static constexpr int TRANSPOSITION_TABLE_SIZE = 0x1000000; // 8-128M:102s, 4-64M:93s 2-32M:91s 1-16M: 冲突
+static constexpr int TRANSPOSITION_TABLE_SIZE = 0x1000000;
 HashMap<Key, TTEntry> TT(TRANSPOSITION_TABLE_SIZE);
 
 #ifdef TRANSPOSITION_TABLE_FAKE_CLEAN
diff --git a/src/uci.cpp b/src/uci.cpp
index 106c4d15..9000db96 100644
--- a/src/uci.cpp
+++ b/src/uci.cpp
@@ -16,19 +16,10 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <cassert>
-#include <iostream>
 #include <sstream>
-#include <string>
 
-#include "evaluate.h"
-#include "movegen.h"
-#include "position.h"
-#include "search.h"
 #include "thread.h"
-#include "tt.h"
 #include "uci.h"
-#include "rule.h"
 
 #ifdef FLUTTER_UI
 #include "command_channel.h"
diff --git a/src/ucioption.cpp b/src/ucioption.cpp
index d22ad9a1..f5380337 100644
--- a/src/ucioption.cpp
+++ b/src/ucioption.cpp
@@ -16,15 +16,10 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#include <algorithm>
-#include <cassert>
-#include <ostream>
 #include <sstream>
 
-#include "misc.h"
-#include "search.h"
+//#include "misc.h"
 #include "thread.h"
-#include "tt.h"
 #include "uci.h"
 #include "option.h"