Formula_14985

\[\delta^{2} \frac{\partial^{2} u_{i}}{\partial t^{2}}=\delta^{2} \frac{\partial}{\partial x_{k}} \lambda_{i k l m}\left(\frac{\partial u_{l}}{\partial x_{m}}+\frac{\partial u_{m}}{\partial x_{l}}+\delta \frac{\partial u_{j}}{\partial x_{l}} \frac{\partial u_{j}}{\partial x_{m}}\right)\]