no. S4
Least Squares Approximations to First Order Elliptic Systems
Publications des séminaires de mathématiques et informatique de Rennes, no. S4 (1977), article no. 11, 14 p. 
@article{PSMIR_1977___S4_A11_0,
     author = {Nitsche, J. A.},
     title = {Least {Squares} {Approximations} to {First} {Order} {Elliptic} {Systems}},
     journal = {Publications des s\'eminaires de math\'ematiques et informatique de Rennes},
     eid = {11},
     pages = {1--14},
     publisher = {D\'epartement de Math\'ematiques et Informatique, Universit\'e de Rennes},
     number = {S4},
     year = {1977},
     language = {en},
     url = {http://www.numdam.org/item/PSMIR_1977___S4_A11_0/}
}
TY  - JOUR
AU  - Nitsche, J. A.
TI  - Least Squares Approximations to First Order Elliptic Systems
JO  - Publications des séminaires de mathématiques et informatique de Rennes
PY  - 1977
SP  - 1
EP  - 14
IS  - S4
PB  - Département de Mathématiques et Informatique, Université de Rennes
UR  - http://www.numdam.org/item/PSMIR_1977___S4_A11_0/
LA  - en
ID  - PSMIR_1977___S4_A11_0
ER  - 
%0 Journal Article
%A Nitsche, J. A.
%T Least Squares Approximations to First Order Elliptic Systems
%J Publications des séminaires de mathématiques et informatique de Rennes
%D 1977
%P 1-14
%N S4
%I Département de Mathématiques et Informatique, Université de Rennes
%U http://www.numdam.org/item/PSMIR_1977___S4_A11_0/
%G en
%F PSMIR_1977___S4_A11_0
Nitsche, J. A. Least Squares Approximations to First Order Elliptic Systems. Publications des séminaires de mathématiques et informatique de Rennes, no. S4 (1977), article  no. 11, 14 p. http://www.numdam.org/item/PSMIR_1977___S4_A11_0/

[1] Haack, W. and G. Hellwig Die Überführung des Randwertproblems für Systeme elliptischer Differentialgleichungen auf Predholmsche Integralgleichungen I. Math. Nachr. 4 (1950-1951), 408-418 | MR | Zbl

[2] Nitsche, J.A. A projection method for Dirichlet-Problems using subspaces with nearly zero boundary conditions in "The mathematical foundations of the finite element method with application to partial differential equations", K. Aziz and I. Babuska eds., Acad. Press, New York and London, 1972, 603-627 | MR | Zbl

[3] Vekua, I.N. Generalized Analytic Functions. Pergarnon Press, Oxford (1962). | MR | Zbl