diff --git a/reasoning_gym/arithmetic/fraction_simplification.py b/reasoning_gym/arithmetic/fraction_simplification.py
index d04c8fa6..0002edcd 100644
--- a/reasoning_gym/arithmetic/fraction_simplification.py
+++ b/reasoning_gym/arithmetic/fraction_simplification.py
@@ -1,7 +1,7 @@
 """Fraction simplification task generator"""
 from dataclasses import dataclass
 from random import Random
-from typing import List, Optional, Tuple
+from typing import Optional, Tuple, Sequence
 from math import gcd
 
 
@@ -12,7 +12,7 @@ class FractionSimplificationConfig:
     max_value: int = 100      # Maximum value for numerator/denominator
     min_factor: int = 2       # Minimum multiplication factor
     max_factor: int = 10      # Maximum multiplication factor
-    styles: List[str] = None  # List of allowed fraction formatting styles
+    styles: Sequence[str] = ("plain", "latex_inline", "latex_frac", "latex_dfrac")  # Allowed fraction formatting styles
     seed: Optional[int] = None
     size: int = 500          # Virtual dataset size
 
@@ -23,10 +23,6 @@ class FractionSimplificationConfig:
         assert self.min_factor >= 2, "min_factor must be at least 2"
         assert self.max_factor >= self.min_factor, "max_factor must be >= min_factor"
         
-        # Set default styles if none provided
-        if self.styles is None:
-            self.styles = ["plain", "latex_inline", "latex_frac", "latex_dfrac"]
-        
         # Validate styles
         valid_styles = {"plain", "latex_inline", "latex_frac", "latex_dfrac"}
         for style in self.styles:
@@ -140,7 +136,7 @@ def fraction_simplification_dataset(
     max_value: int = 100,
     min_factor: int = 2,
     max_factor: int = 10,
-    styles: List[str] = None,
+    styles: Sequence[str] = ("plain", "latex_inline", "latex_frac", "latex_dfrac"),
     seed: Optional[int] = None,
     size: int = 500,
 ) -> FractionSimplificationDataset: