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3. W. Prager, Variational principles of linear elastostatics for discontinous displacements, strains, and stresses, Recent Progress in Applied Mechanics; the Folke Odqvist Volume, Stockholm, 1969, pp. 463?474.
4. Pedro V. Marcal, Finite-element analysis of combined problems of non-linear material and geometric behavior, Computational Approaches in Applied Mechanics (ASME Computer Conference, Chicago, 1969), The American Society of Mechanical Engineers, New York, 1970, pp. 133?149.