1. Ein Gegenstück zum Ritzschen Verfahren;Trefftz,1926
2. The Mathematical Theory of Elasticity;Trefftz,1934
3. Variational Methods of Mathematical Physics;Mikhlin,1957
4. Polyharmonic Polynomials;Bondarkenko,1968
5. Special Classes of Functions in the Anisotropic Theory of Elasticity;Frolov,1981