+/** Create an epsilon tensor in a Euclidean space with three indices. The
+ * indices must be of class idx or a subclass, and have a dimension of 3.
+ *
+ * @param i1 First index
+ * @param i2 Second index
+ * @param i3 Third index
+ * @return newly constructed epsilon tensor */
+ex epsilon_tensor(const ex & i1, const ex & i2, const ex & i3);
+
+/** Create an epsilon tensor in a Minkowski space with four indices. The
+ * indices must be of class varidx or a subclass, and have a dimension of 4.
+ *
+ * @param i1 First index
+ * @param i2 Second index
+ * @param i3 Third index
+ * @param i4 Fourth index
+ * @param pos_sig Whether the signature of the metric is positive
+ * @return newly constructed epsilon tensor */
+ex lorentz_eps(const ex & i1, const ex & i2, const ex & i3, const ex & i4, bool pos_sig = false);
+