The Israel equations for thin shells in General Relativity are derived directly from the least action principle. The method is elaborated for obtaining the equations for double layers in quadratic gravity from the least action principle.

中文翻译：

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二次重力中的双层和最小作用原理

广义相对论中薄壳的以色列方程式是直接从最小作用原理导出的。阐述了从最小作用原理获得二次重力双层方程的方法。