A complete asymptotic expansion of the spectral function of second order elliptic operators in $\mathbf R^n$

A complete asymptotic expansion as $\lambda\to\infty$, $|x|,|y|\leqslant b<\infty$ ($b$ arbitrary) is obtained for the spectral function $e_\lambda(x,y)$ of second order elliptic operators in $\mathbf R^n$ satisfying the condition of not being “trapped”, i.e. the requirement that the bicharacteristics issuing from any point extend to infinity.
Bibliography: 17 titles.