Differential geometry, calculus of variations, and their applications - Rassias, George M., 1953-; Rassias, Themistocles M., 1951-; Ρασσιάς, Γεώργιος Μ.; Ρασσιάς, Θεμιστοκλής Μ (Lecture notes in pure and applied mathematics. Pure and applied mathematics, 1985)