diff --git a/Projects/2_Classical Planning/layers.py b/Projects/2_Classical Planning/layers.py
index da399266..56117692 100644
--- a/Projects/2_Classical Planning/layers.py	
+++ b/Projects/2_Classical Planning/layers.py	
@@ -2,8 +2,12 @@
 from copy import deepcopy
 from functools import lru_cache
 from itertools import combinations
-from collections import defaultdict, MutableSet
-
+try:
+    from collections import defaultdict, MutableSet
+except ImportError:
+    from collections.abc import MutableSet
+    from collections import defaultdict
+    
 from aimacode.planning import Action
 from aimacode.utils import expr, Expr