diff --git a/src/ui/flutter_app/lib/common/algorithm.dart b/src/ui/flutter_app/lib/common/algorithm.dart
deleted file mode 100644
index 579eaba0..00000000
--- a/src/ui/flutter_app/lib/common/algorithm.dart
+++ /dev/null
@@ -1,35 +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/>.
-*/
-
-abs(value) => value > 0 ? value : -value;
-
-int binarySearch(List<int> array, int start, int end, int key) {
-  if (start > end) return -1;
-
-  if (array[start] == key) return start;
-  if (array[end] == key) return end;
-
-  final middle = start + (end - start) ~/ 2;
-  if (array[middle] == key) return middle;
-
-  if (key < array[middle]) {
-    return binarySearch(array, start + 1, middle - 1, key);
-  }
-
-  return binarySearch(array, middle + 1, end - 1, key);
-}
diff --git a/src/ui/flutter_app/lib/mill/types.dart b/src/ui/flutter_app/lib/mill/types.dart
index c4fa621f..7f0aaf20 100644
--- a/src/ui/flutter_app/lib/mill/types.dart
+++ b/src/ui/flutter_app/lib/mill/types.dart
@@ -16,7 +16,7 @@
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-import 'package:sanmill/common/algorithm.dart';
+abs(value) => value > 0 ? value : -value;
 
 enum MoveType { place, move, remove }