1. Approximate Methods of Higher Analysis;Kantorovich,1964
2. Variational Methods of Mathematical Physics;Mikhlin,1964
3. Variational Methods in Mathematics, Science and Engineering;Rektorys,1980
4. Les Méthodes Directes en Théorie des Equations Elliptiques;Necas,1967
5. Variational Methods in Mathematical Physics;Blanchard,1992