diff --git a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/IEnvironmentState.cs b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/IEnvironmentState.cs
index 72b02722c..8690196e2 100644
--- a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/IEnvironmentState.cs
+++ b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/IEnvironmentState.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Canaan Inc. All rights reserved.
+// Copyright (c) Canaan Inc. All rights reserved.
 // Licensed under the Apache license. See LICENSE file in the project root for full license information.
 
 using System;
diff --git a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/SearchNode.cs b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/SearchNode.cs
index 4bb00fc81..6770704ef 100644
--- a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/SearchNode.cs
+++ b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/SearchNode.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Canaan Inc. All rights reserved.
+// Copyright (c) Canaan Inc. All rights reserved.
 // Licensed under the Apache license. See LICENSE file in the project root for full license information.
 
 using System;
diff --git a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/Searcher.cs b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/Searcher.cs
index 8e88713b8..382d0bd27 100644
--- a/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/Searcher.cs
+++ b/src/Nncase.Schedule/Schedule/MonteCarloTreeSearch/Searcher.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Canaan Inc. All rights reserved.
+// Copyright (c) Canaan Inc. All rights reserved.
 // Licensed under the Apache license. See LICENSE file in the project root for full license information.
 
 using System;
diff --git a/src/Nncase.Schedule/Schedule/TileGraph/GraphMCTS.cs b/src/Nncase.Schedule/Schedule/TileGraph/GraphMCTS.cs
index 99f388d70..b3032241f 100644
--- a/src/Nncase.Schedule/Schedule/TileGraph/GraphMCTS.cs
+++ b/src/Nncase.Schedule/Schedule/TileGraph/GraphMCTS.cs
@@ -1,4 +1,4 @@
-// Copyright (c) Canaan Inc. All rights reserved.
+// Copyright (c) Canaan Inc. All rights reserved.
 // Licensed under the Apache license. See LICENSE file in the project root for full license information.
 
 using System.Collections;
@@ -33,7 +33,7 @@ public sealed class MCTState : IEnvironmentState<MergePoint>
 
     private int _permformCount;
 
-    private TieredTileGraph _graph;
+    private readonly TieredTileGraph _graph;
 
     public MCTState(TieredTileGraph graph, string moduleKind, string prefix, string searchPath, Dictionary<TileNode, GraphTiler.TiledFunc> solveMemo, ICpuTargetOptions targetOptions)
     {