| Multiple solutions of second ordered nonlinear elliptic boundary value problems are studied in this thesis and the study is divided into three parts.;At the first, multiple solutions of second ordered semi-linear elliptic boundary value problems are obtained with two pairs of quasi-supersolutions and quasi-subsolutions. The result is a generalization of the one of Herbert Amann.;At the second, as one application of the first result, the existence of several ordered positive solution of singularly perturbed semi-linear elliptic Dirichlet boundary value problems is studied. The result is a generalization of the one of De Figuerido.;At the third, as another application of the first result, the existence of several ordered positive solutions of singularly perturbed semi-linear elliptic Neumann or Robin boundary value problems is studied. |
