diff --git a/CMakeLists.txt b/CMakeLists.txt
index d9eb054..370ee7a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,7 +8,7 @@ include(FetchContent)
 FetchContent_Declare(
     chesslib
     GIT_REPOSITORY https://github.com/winapiadmin/chesslib.git
-    GIT_TAG maintaince_1
+    GIT_TAG 46-null-move-modification-fix
 )
 FetchContent_MakeAvailable(chesslib)
 add_executable(engine "main.cpp" "timeman.cpp" "timeman.h" "eval.h" "eval.cpp" "tune.h" "ucioption.h" "tune.cpp" "ucioption.cpp" "tt.h" "tt.cpp" "uci.cpp" "uci.h" "search.h" "search.cpp" "score.h" "score.cpp" "movepick.h" "movepick.cpp")
diff --git a/eval.h b/eval.h
index eb881e6..74c1e20 100644
--- a/eval.h
+++ b/eval.h
@@ -1,6 +1,4 @@
 #pragma once
-#include <cstdint>
-#include <cstdlib>
 #include <fwd_decl.h>
 using Value = int;
 namespace engine {
diff --git a/score.cpp b/score.cpp
index 2fdc2c5..2d07d9e 100644
--- a/score.cpp
+++ b/score.cpp
@@ -1,5 +1,6 @@
 #include "score.h"
 #include <cassert>
+#include <cmath>
 namespace engine {
 Score::Score(Value v) {
   assert(-VALUE_INFINITE < v && v < VALUE_INFINITE);
@@ -14,4 +15,4 @@ Score::Score(Value v) {
     score = (v > 0) ? Mate{distance} : Mate{-distance};
   }
 }
-} // namespace engine
\ No newline at end of file
+} // namespace engine
diff --git a/search.cpp b/search.cpp
index 07b9af5..4d33b3f 100644
--- a/search.cpp
+++ b/search.cpp
@@ -6,14 +6,12 @@
 #include <atomic>
 #include <moves_io.h>
 #include <position.h>
+#include <printers.h>
 using namespace chess;
 namespace engine {
 TranspositionTable search::tt(16);
 std::atomic<bool> stopSearch{false};
-void search::stop() {
-  tt.clear();
-  stopSearch.store(true, std::memory_order_relaxed);
-}
+void search::stop() { stopSearch.store(true, std::memory_order_relaxed); }
 struct Session {
   timeman::TimeManagement tm;
   timeman::LimitsType tc;
@@ -29,7 +27,11 @@ void update_pv(Move *pv, Move move, const Move *childPv) {
 }
 Value qsearch(Board &board, Value alpha, Value beta, Session &session,
               int ply = 0) {
+  if (session.tm.elapsed() >= session.tm.optimum() ||
+      stopSearch.load(std::memory_order_relaxed))
+    return VALUE_NONE;
   session.nodes++;
+  session.seldepth = std::max(session.seldepth, ply);
   int standPat = eval::eval(board);
   Value maxScore = standPat;
   if (maxScore >= beta)
@@ -40,8 +42,11 @@ Value qsearch(Board &board, Value alpha, Value beta, Session &session,
   board.legals<MoveGenType::CAPTURE>(moves);
   for (Move move : moves) {
     board.doMove(move);
-    Value score = -qsearch(board, -beta, -alpha, session, ply + 1);
+    Value score = qsearch(board, -beta, -alpha, session, ply + 1);
     board.undoMove();
+    if (score == VALUE_NONE)
+      return VALUE_NONE;
+    score = -score;
     if (score >= beta)
       return score;
     if (score > maxScore)
@@ -97,7 +102,7 @@ Value doSearch(Board &board, int depth, Value alpha, Value beta,
     preferred = Move(entry->getMove());
   }
   if (depth == 0) {
-    return qsearch(board, alpha, beta, session, ply + 1);
+    return qsearch(board, alpha, beta, session, ply);
   }
   Value maxScore = -VALUE_INFINITE;
   Movelist moves;
@@ -107,16 +112,26 @@ Value doSearch(Board &board, int depth, Value alpha, Value beta,
     return board.checkers() ? -MATE(ply) : 0;
   }
   movepick::orderMoves(board, moves, preferred, ply);
-  for (Move move : moves) {
+  if (bool useNMP = depth >= 3 && !board.checkers() && ply > 0) {
+    int R = 2 + depth / 6;
+    board.doNullMove();
+    Value score =
+        doSearch(board, depth - 1 - R, -beta, -beta + 1, session, ply + 1);
 
+    if (score == VALUE_NONE)
+      return VALUE_NONE;
+    score = -score;
+    board.undoMove();
+    if (score >= beta)
+      return beta;
+  }
+  for (Move move : moves) {
     board.doMove(move);
-
     Value childScore =
         doSearch(board, depth - 1, -beta, -alpha, session, ply + 1);
 
     board.undoMove();
 
-    // ---- ABORT PROPAGATION ----
     if (childScore == VALUE_NONE)
       return VALUE_NONE;
 
@@ -165,6 +180,7 @@ Value doSearch(Board &board, int depth, Value alpha, Value beta,
 }
 void search::search(const chess::Board &board,
                     const timeman::LimitsType timecontrol) {
+  stopSearch = false;
   static double originalTimeAdjust = -1;
   Session session;
   session.tc = timecontrol;
@@ -183,7 +199,7 @@ void search::search(const chess::Board &board,
     Value score_ =
         doSearch(board_, i, -VALUE_INFINITE, VALUE_INFINITE, session);
     if (session.tm.elapsed() >= session.tm.optimum() ||
-        stopSearch.load(std::memory_order_relaxed) || score_ == VALUE_NONE)
+        stopSearch.load(std::memory_order_relaxed) || abs(score_) == VALUE_NONE)
       break;
     InfoFull info{};
     info.depth = i;
@@ -195,6 +211,18 @@ void search::search(const chess::Board &board,
     info.timeMs = session.tm.elapsed();
     info.multiPV = 1;
     info.score = score_;
+    TTEntry *entry = tt.lookup(board.hash());
+    if (entry)
+      switch (entry->getFlag()) {
+      case LOWERBOUND:
+        info.bound = "lowerbound";
+        break;
+      case UPPERBOUND:
+        info.bound = "upperbound";
+        break;
+      default:
+        break;
+      }
     std::string pv = "";
     for (Move *m = session.pv[0]; *m != Move::none(); m++)
       pv += chess::uci::moveToUci(*m, board.chess960()) + " ";
@@ -233,7 +261,7 @@ void search::search(const chess::Board &board,
         info.nodes = 1;
         info.score = 0;
         info.multiPV = 1;
-        info.pv = chess::uci::moveToUci(best, board.chess960());
+        info.pv = std::string(chess::uci::moveToUci(best, board.chess960()));
         report(info);
 
         report(chess::uci::moveToUci(best, board.chess960()));
diff --git a/tt.cpp b/tt.cpp
index bd400ef..f084236 100644
--- a/tt.cpp
+++ b/tt.cpp
@@ -68,7 +68,7 @@ TTEntry *TranspositionTable::lookup(uint64_t hash) {
   TTEntry &e0 = table[index], &e1 = table[index + 1];
   // Check the entries
   for (TTEntry *e : {&e0, &e1}) {
-    if (e->key == hash)
+    if (e->key == hash && e->getGeneration() == this->time)
       return e;
   }
   return nullptr;
diff --git a/tt.h b/tt.h
index f2e2496..6c69dc3 100644
--- a/tt.h
+++ b/tt.h
@@ -37,8 +37,8 @@ struct TTEntry {
                                        << GEN_SHIFT;
 
   // getters
-  inline uint16_t getScore() const noexcept {
-    return static_cast<uint16_t>((pack & SCORE_MASK) >> SCORE_SHIFT);
+  inline int16_t getScore() const noexcept {
+    return static_cast<int16_t>((pack & SCORE_MASK) >> SCORE_SHIFT);
   }
 
   inline uint8_t getDepth() const noexcept {
@@ -176,4 +176,4 @@ class TranspositionTable {
     return (used * 1000) / buckets;
   }
 };
-} // namespace engine
\ No newline at end of file
+} // namespace engine
diff --git a/uci.cpp b/uci.cpp
index 4ee298b..5025555 100644
--- a/uci.cpp
+++ b/uci.cpp
@@ -5,7 +5,9 @@
 #include <algorithm>
 #include <iostream>
 #include <position.h>
+#include <printers.h>
 #include <sstream>
+#include <thread>
 using namespace engine;
 chess::Position pos;
 OptionsMap engine::options;
@@ -69,7 +71,18 @@ timeman::LimitsType parse_limits(std::istream &is) {
 
   return limits;
 }
-void handleGo(std::istringstream &ss) { search::search(pos, parse_limits(ss)); }
+std::thread searchThread;
+
+void handleGo(std::istringstream &ss) {
+  if (searchThread.joinable()) {
+    search::stop();
+    searchThread.join();
+  }
+
+  searchThread = std::thread([ss = std::move(ss)]() mutable {
+    search::search(pos, parse_limits(ss));
+  });
+}
 template <typename... Ts> struct overload : Ts... {
   using Ts::operator()...;
 };
@@ -159,7 +172,7 @@ void engine::loop() {
         break;
       } else if (token == "position") {
         handlePosition(ss);
-        break; // rest belongs to position
+        break;
       } else if (token == "go") {
         handleGo(ss);
         break; // rest belongs to go
@@ -168,8 +181,13 @@ void engine::loop() {
         break;
       } else if (token == "stop") {
         search::stop();
+        if (searchThread.joinable())
+          searchThread.join();
         break;
       } else if (token == "quit") {
+        search::stop();
+        if (searchThread.joinable())
+          searchThread.join();
         return;
       } else if (token == "setoption") {
         options.setoption(ss);