I'm proving theorem 2 occurring in Sunada's paper Riemannian coverings and isospectral manifolds. Unfortunately Sunada's quotes himself to the following paper:
Tchbotarev’s density theorem for closed geodesics in a compact locally symmetric space of negative curvature. Preprint.
which I'm unable to find. Is there anybody which known the Sunada's works and can help me? Maybe such article was published with another name...
Alternatively, if there is someone which well know the theory of closed geodesic decomposition under Riemannian covering, I can try to explain the point which I not understand.
Thanks in advance.