diff --git a/src/ui/flutter_app/lib/engine/native_engine.dart b/src/ui/flutter_app/lib/engine/native_engine.dart
index 90f2f273..8cb57d40 100644
--- a/src/ui/flutter_app/lib/engine/native_engine.dart
+++ b/src/ui/flutter_app/lib/engine/native_engine.dart
@@ -20,7 +20,7 @@ import 'dart:async';
 
 import 'package:flutter/services.dart';
 import 'package:sanmill/common/config.dart';
-import 'package:sanmill/mill/mill.dart';
+import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/mill/position.dart';
 
 import 'engine.dart';
diff --git a/src/ui/flutter_app/lib/mill/game.dart b/src/ui/flutter_app/lib/mill/game.dart
index 853d9e3a..65da98d6 100644
--- a/src/ui/flutter_app/lib/mill/game.dart
+++ b/src/ui/flutter_app/lib/mill/game.dart
@@ -19,7 +19,6 @@
 import 'package:sanmill/common/config.dart';
 import 'package:sanmill/engine/engine.dart';
 
-import 'mill.dart';
 import 'position.dart';
 import 'types.dart';
 
diff --git a/src/ui/flutter_app/lib/mill/mill.dart b/src/ui/flutter_app/lib/mill/mill.dart
deleted file mode 100644
index 01ccaadc..00000000
--- a/src/ui/flutter_app/lib/mill/mill.dart
+++ /dev/null
@@ -1,203 +0,0 @@
-/*
-  This file is part of Sanmill.
-  Copyright (C) 2019-2021 The Sanmill developers (see AUTHORS file)
-
-  Sanmill is free software: you can redistribute it and/or modify
-  it under the terms of the GNU General Public License as published by
-  the Free Software Foundation, either version 3 of the License, or
-  (at your option) any later version.
-
-  Sanmill is distributed in the hope that it will be useful,
-  but WITHOUT ANY WARRANTY; without even the implied warranty of
-  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-  GNU General Public License for more details.
-
-  You should have received a copy of the GNU General Public License
-  along with this program.  If not, see <http://www.gnu.org/licenses/>.
-*/
-
-import 'types.dart';
-
-Map<int, int> squareToIndex = {
-  8: 17,
-  9: 18,
-  10: 25,
-  11: 32,
-  12: 31,
-  13: 30,
-  14: 23,
-  15: 16,
-  16: 10,
-  17: 12,
-  18: 26,
-  19: 40,
-  20: 38,
-  21: 36,
-  22: 22,
-  23: 8,
-  24: 3,
-  25: 6,
-  26: 27,
-  27: 48,
-  28: 45,
-  29: 42,
-  30: 21,
-  31: 0
-};
-
-Map<int, int> indexToSquare = squareToIndex.map((k, v) => MapEntry(v, k));
-
-int makeSquare(int file, int rank) {
-  return (file << 3) + rank - 1;
-}
-
-enum GameResult { pending, win, lose, draw, none }
-
-class PieceColor {
-  static const none = '*';
-  static const black = '@';
-  static const white = 'O';
-  static const ban = 'X';
-  static const nobody = '-';
-  static const draw = '=';
-
-  static String of(String piece) {
-    if (black.contains(piece)) return black;
-    if (white.contains(piece)) return white;
-    if (ban.contains(piece)) return ban;
-    return nobody;
-  }
-
-  static bool isSameColor(String p1, String p2) {
-    return of(p1) == of(p2);
-  }
-
-  static String opponent(String color) {
-    if (color == white) return black;
-    if (color == black) return white;
-    return color;
-  }
-
-  String operator -(String c) => opponent(c);
-}
-
-class Piece {
-  static const noPiece = PieceColor.none;
-  static const blackStone = PieceColor.black;
-  static const whiteStone = PieceColor.white;
-  static const ban = PieceColor.ban;
-
-  static bool isEmpty(String c) => noPiece.contains(c);
-  static bool isBlack(String c) => blackStone.contains(c);
-  static bool isWhite(String c) => whiteStone.contains(c);
-  static bool isBan(String c) => ban.contains(c);
-}
-
-class Move {
-  static const invalidMove = -1;
-
-  // Square
-  int from = 0;
-  int to = 0;
-
-  // file & rank
-  int fromFile = 0;
-  int fromRank = 0;
-  int toFile = 0;
-  int toRank = 0;
-
-  // Index
-  int fromIndex = 0;
-  int toIndex = 0;
-
-  String removed = Piece.noPiece;
-
-  // 'move' is the UCI engine's move-string
-  String? move = "";
-
-  MoveType type = MoveType.none;
-
-  // Used to restore fen step conter when regreting
-  String counterMarks = "";
-
-  parse() {
-    if (!legal(move)) {
-      throw "Error: Invalid Move: $move";
-    }
-
-    if (move![0] == '-' && move!.length == "-(1,2)".length) {
-      type = MoveType.remove;
-      from = fromFile = fromRank = fromIndex = invalidMove;
-      toFile = int.parse(move![2]);
-      toRank = int.parse(move![4]);
-      //captured = Piece.noPiece;
-    } else if (move!.length == "(1,2)->(3,4)".length) {
-      type = MoveType.move;
-      fromFile = int.parse(move![1]);
-      fromRank = int.parse(move![3]);
-      from = makeSquare(fromFile, fromRank);
-      fromIndex = squareToIndex[from] ?? invalidMove;
-      toFile = int.parse(move![8]);
-      toRank = int.parse(move![10]);
-      removed = Piece.noPiece;
-    } else if (move!.length == "(1,2)".length) {
-      type = MoveType.place;
-      from = fromFile = fromRank = fromIndex = invalidMove;
-      toFile = int.parse(move![1]);
-      toRank = int.parse(move![3]);
-      removed = Piece.noPiece;
-    } else if (move == "draw") {
-      // TODO
-      print("Computer request draw");
-    } else {
-      assert(false);
-    }
-
-    to = makeSquare(toFile, toRank);
-    toIndex = squareToIndex[to] ?? invalidMove;
-  }
-
-  Move(this.move) {
-    parse();
-  }
-
-  /// Format:
-  /// Place: (1,2)
-  /// Remove: -(1,2)
-  /// Move: (3,1)->(2,1)
-
-  Move.set(String move) {
-    this.move = move;
-    parse();
-  }
-
-  static bool legal(String? move) {
-    if (move == "draw") {
-      return true; // TODO
-    }
-
-    if (move == null || move.length > "(3,1)->(2,1)".length) return false;
-
-    String range = "0123456789(,)->";
-
-    if (!(move[0] == '(' || move[0] == '-')) {
-      return false;
-    }
-
-    if (move[move.length - 1] != ')') {
-      return false;
-    }
-
-    for (int i = 0; i < move.length; i++) {
-      if (!range.contains(move[i])) return false;
-    }
-
-    if (move.length == "(3,1)->(2,1)".length) {
-      if (move.substring(0, 4) == move.substring(7, 11)) {
-        return false;
-      }
-    }
-
-    return true;
-  }
-}
diff --git a/src/ui/flutter_app/lib/mill/position.dart b/src/ui/flutter_app/lib/mill/position.dart
index 04b07d8d..843e22dc 100644
--- a/src/ui/flutter_app/lib/mill/position.dart
+++ b/src/ui/flutter_app/lib/mill/position.dart
@@ -17,7 +17,7 @@
 */
 
 import 'package:sanmill/mill/game.dart';
-import 'package:sanmill/mill/mill.dart';
+import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/mill/recorder.dart';
 import 'package:sanmill/mill/rule.dart';
 import 'package:sanmill/services/audios.dart';
diff --git a/src/ui/flutter_app/lib/mill/recorder.dart b/src/ui/flutter_app/lib/mill/recorder.dart
index 8578358a..080f0c17 100644
--- a/src/ui/flutter_app/lib/mill/recorder.dart
+++ b/src/ui/flutter_app/lib/mill/recorder.dart
@@ -16,7 +16,6 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-import 'mill.dart';
 import 'position.dart';
 import 'types.dart';
 
diff --git a/src/ui/flutter_app/lib/mill/types.dart b/src/ui/flutter_app/lib/mill/types.dart
index 2658cbcb..2064fa0e 100644
--- a/src/ui/flutter_app/lib/mill/types.dart
+++ b/src/ui/flutter_app/lib/mill/types.dart
@@ -18,8 +18,143 @@
 
 abs(value) => value > 0 ? value : -value;
 
+class Move {
+  static const invalidMove = -1;
+
+  // Square
+  int from = 0;
+  int to = 0;
+
+  // file & rank
+  int fromFile = 0;
+  int fromRank = 0;
+  int toFile = 0;
+  int toRank = 0;
+
+  // Index
+  int fromIndex = 0;
+  int toIndex = 0;
+
+  String removed = Piece.noPiece;
+
+  // 'move' is the UCI engine's move-string
+  String? move = "";
+
+  MoveType type = MoveType.none;
+
+  // Used to restore fen step conter when regreting
+  String counterMarks = "";
+
+  parse() {
+    if (!legal(move)) {
+      throw "Error: Invalid Move: $move";
+    }
+
+    if (move![0] == '-' && move!.length == "-(1,2)".length) {
+      type = MoveType.remove;
+      from = fromFile = fromRank = fromIndex = invalidMove;
+      toFile = int.parse(move![2]);
+      toRank = int.parse(move![4]);
+      //captured = Piece.noPiece;
+    } else if (move!.length == "(1,2)->(3,4)".length) {
+      type = MoveType.move;
+      fromFile = int.parse(move![1]);
+      fromRank = int.parse(move![3]);
+      from = makeSquare(fromFile, fromRank);
+      fromIndex = squareToIndex[from] ?? invalidMove;
+      toFile = int.parse(move![8]);
+      toRank = int.parse(move![10]);
+      removed = Piece.noPiece;
+    } else if (move!.length == "(1,2)".length) {
+      type = MoveType.place;
+      from = fromFile = fromRank = fromIndex = invalidMove;
+      toFile = int.parse(move![1]);
+      toRank = int.parse(move![3]);
+      removed = Piece.noPiece;
+    } else if (move == "draw") {
+      // TODO
+      print("Computer request draw");
+    } else {
+      assert(false);
+    }
+
+    to = makeSquare(toFile, toRank);
+    toIndex = squareToIndex[to] ?? invalidMove;
+  }
+
+  Move(this.move) {
+    parse();
+  }
+
+  /// Format:
+  /// Place: (1,2)
+  /// Remove: -(1,2)
+  /// Move: (3,1)->(2,1)
+
+  Move.set(String move) {
+    this.move = move;
+    parse();
+  }
+
+  static bool legal(String? move) {
+    if (move == "draw") {
+      return true; // TODO
+    }
+
+    if (move == null || move.length > "(3,1)->(2,1)".length) return false;
+
+    String range = "0123456789(,)->";
+
+    if (!(move[0] == '(' || move[0] == '-')) {
+      return false;
+    }
+
+    if (move[move.length - 1] != ')') {
+      return false;
+    }
+
+    for (int i = 0; i < move.length; i++) {
+      if (!range.contains(move[i])) return false;
+    }
+
+    if (move.length == "(3,1)->(2,1)".length) {
+      if (move.substring(0, 4) == move.substring(7, 11)) {
+        return false;
+      }
+    }
+
+    return true;
+  }
+}
+
 enum MoveType { place, move, remove, none }
 
+class PieceColor {
+  static const none = '*';
+  static const black = '@';
+  static const white = 'O';
+  static const ban = 'X';
+  static const nobody = '-';
+  static const draw = '=';
+
+  static String of(String piece) {
+    if (black.contains(piece)) return black;
+    if (white.contains(piece)) return white;
+    if (ban.contains(piece)) return ban;
+    return nobody;
+  }
+
+  static bool isSameColor(String p1, String p2) => of(p1) == of(p2);
+
+  static String opponent(String color) {
+    if (color == white) return black;
+    if (color == black) return white;
+    return color;
+  }
+
+  String operator -(String c) => opponent(c);
+}
+
 enum Phase { none, ready, placing, moving, gameOver }
 
 enum Act { none, select, place, remove }
@@ -38,6 +173,18 @@ enum GameOverReason {
 
 enum PieceType { none, blackStone, whiteStone, ban, count, stone }
 
+class Piece {
+  static const noPiece = PieceColor.none;
+  static const blackStone = PieceColor.black;
+  static const whiteStone = PieceColor.white;
+  static const ban = PieceColor.ban;
+
+  static bool isEmpty(String c) => noPiece.contains(c);
+  static bool isBlack(String c) => blackStone.contains(c);
+  static bool isWhite(String c) => whiteStone.contains(c);
+  static bool isBan(String c) => ban.contains(c);
+}
+
 enum Square {
   SQ_0,
   SQ_1,
@@ -96,7 +243,9 @@ enum Rank { rank_1, rank_2, rank_3, rank_4, rank_5, rank_6, rank_7, rank_8 }
 
 const rankNumber = 8;
 
-const invalidIndex = -1;
+int makeSquare(int file, int rank) {
+  return (file << 3) + rank - 1;
+}
 
 bool isOk(int sq) {
   bool ret = (sq == 0 || (sq >= sqBegin && sq < sqEnd));
@@ -129,3 +278,36 @@ int toSq(int move) {
 int makeMove(int from, int to) {
   return (from << 8) + to;
 }
+
+const invalidIndex = -1;
+
+Map<int, int> squareToIndex = {
+  8: 17,
+  9: 18,
+  10: 25,
+  11: 32,
+  12: 31,
+  13: 30,
+  14: 23,
+  15: 16,
+  16: 10,
+  17: 12,
+  18: 26,
+  19: 40,
+  20: 38,
+  21: 36,
+  22: 22,
+  23: 8,
+  24: 3,
+  25: 6,
+  26: 27,
+  27: 48,
+  28: 45,
+  29: 42,
+  30: 21,
+  31: 0
+};
+
+Map<int, int> indexToSquare = squareToIndex.map((k, v) => MapEntry(v, k));
+
+enum GameResult { pending, win, lose, draw, none }
diff --git a/src/ui/flutter_app/lib/painting/board_painter.dart b/src/ui/flutter_app/lib/painting/board_painter.dart
index 7ac54e5f..4b3bc7b9 100644
--- a/src/ui/flutter_app/lib/painting/board_painter.dart
+++ b/src/ui/flutter_app/lib/painting/board_painter.dart
@@ -19,7 +19,6 @@
 import 'package:flutter/material.dart';
 import 'package:sanmill/common/config.dart';
 import 'package:sanmill/mill/game.dart';
-import 'package:sanmill/mill/mill.dart';
 import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/style/app_theme.dart';
 
diff --git a/src/ui/flutter_app/lib/painting/pieces_painter.dart b/src/ui/flutter_app/lib/painting/pieces_painter.dart
index 9732fd24..82d112d0 100644
--- a/src/ui/flutter_app/lib/painting/pieces_painter.dart
+++ b/src/ui/flutter_app/lib/painting/pieces_painter.dart
@@ -18,7 +18,6 @@
 
 import 'package:flutter/material.dart';
 import 'package:sanmill/common/config.dart';
-import 'package:sanmill/mill/mill.dart';
 import 'package:sanmill/mill/position.dart';
 import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/style/app_theme.dart';
diff --git a/src/ui/flutter_app/lib/widgets/game_page.dart b/src/ui/flutter_app/lib/widgets/game_page.dart
index 12700c57..89b401fc 100644
--- a/src/ui/flutter_app/lib/widgets/game_page.dart
+++ b/src/ui/flutter_app/lib/widgets/game_page.dart
@@ -26,7 +26,6 @@ import 'package:sanmill/engine/native_engine.dart';
 import 'package:sanmill/generated/l10n.dart';
 import 'package:sanmill/main.dart';
 import 'package:sanmill/mill/game.dart';
-import 'package:sanmill/mill/mill.dart';
 import 'package:sanmill/mill/types.dart';
 import 'package:sanmill/services/audios.dart';
 import 'package:sanmill/style/app_theme.dart';