diff --git a/mars/optimization/logical/core.py b/mars/optimization/logical/core.py
index af9b8f1e91..9f99def5d6 100644
--- a/mars/optimization/logical/core.py
+++ b/mars/optimization/logical/core.py
@@ -134,7 +134,7 @@ def _replace_node(self, original_node: EntityType, new_node: EntityType):
     def _replace_subgraph(
         self,
         graph: Optional[EntityGraph],
-        removed_nodes: Optional[Set[EntityType]],
+        nodes_to_remove: Optional[Set[EntityType]],
         new_results: Optional[List[Entity]] = None,
     ):
         """
@@ -146,7 +146,7 @@ def _replace_subgraph(
         ----------
         graph : EntityGraph, optional
             The input graph. If it's none, no new node and edge will be added.
-        removed_nodes : Set[EntityType], optional
+        nodes_to_remove : Set[EntityType], optional
             The nodes to be removed. All the edges connected with them are removed as well.
         new_results : List[EntityType], optional, default None
             The updated results of the graph. If it's None, then the results will not be updated.
@@ -160,18 +160,18 @@ def _replace_subgraph(
         affected_successors = set()
 
         output_to_node = dict()
-        removed_nodes = removed_nodes or set()
+        nodes_to_remove = nodes_to_remove or set()
         if graph is not None:
             # Add the output key -> node of the subgraph
             for node in graph.iter_nodes():
-                if node in removed_nodes:
+                if node in nodes_to_remove:
                     raise ValueError(f"The node {node} is in the removed set")
                 for output in node.outputs:
                     output_to_node[output.key] = node
 
-        for node in removed_nodes:
+        for node in nodes_to_remove:
             for affected_successor in self._graph.iter_successors(node):
-                if affected_successor not in removed_nodes:
+                if affected_successor not in nodes_to_remove:
                     affected_successors.add(affected_successor)
         # Check whether affected successors' inputs are in subgraph
         for affected_successor in affected_successors:
@@ -180,7 +180,7 @@ def _replace_subgraph(
                     raise ValueError(
                         f"The output {inp} of node {affected_successor} is missing in the subgraph"
                     )
-        for node in removed_nodes:
+        for node in nodes_to_remove:
             self._graph.remove_node(node)
 
         if graph is None:
@@ -200,7 +200,7 @@ def _replace_subgraph(
                 self._graph.add_edge(pred_node, node)
 
         if new_results is not None:
-            self._graph.results = new_results.copy()
+            self._graph.results = list(new_results)
 
     def _add_collapsable_predecessor(self, node: EntityType, predecessor: EntityType):
         pred_original = self._records.get_original_entity(predecessor, predecessor)