1. Sobolev Spaces;Adams,1975
2. A finite element method for a boundary value problem of mixed type;Aziz;Numer. Math.,1984
3. About a class of quasilinear equations of mixed type;Gvazava;Akad. Nauk Gruzinskoi SSR,1981
4. Lectures on Partial and Pfaffian Differential Equations;Haack,1972
5. Function Spaces;Kufner,1977