diff --git a/pyerrors/input/hadrons.py b/pyerrors/input/hadrons.py
index efe4feb1..e139f2b2 100644
--- a/pyerrors/input/hadrons.py
+++ b/pyerrors/input/hadrons.py
@@ -298,6 +298,18 @@ def read_Fourquark_hd5(path, filestem, ens_id, idl=None, vertices=["VA", "AV"]):
     return result_dict
 
 
+def _epsilon_tensor(i, j, k, o):
+    """Rank-4 epsilon tensor
+
+    Extension of https://codegolf.stackexchange.com/a/160375
+    """
+    test_set = set((i, j, k, o))
+    if not (test_set <= set((1, 2, 3, 4)) or test_set <= set((0, 1, 2, 3))):
+        raise Exception("Unexpected input", i, j, k, o)
+
+    return (i - j) * (j - k) * (k - i) * (i - o) * (j - o) * (o - k) / 12
+
+
 def _get_lorentz_names(name):
     assert len(name) == 2