exvector get_dummy_indices() const;
/** Return a vector containing the dummy indices in the contraction with
- * another indexed object. */
+ * another indexed object. This is symmetric: a.get_dummy_indices(b)
+ * == b.get_dummy_indices(a) */
exvector get_dummy_indices(const indexed & other) const;
/** Check whether the object has an index that forms a dummy index pair