@article{NUMA_1977__28_132486,
     author = {G.J. Fix and M.E. Gurtin},
     title = {On {Patched} {Variational} {Principles} with {Application} to {Elliptic} and {Mixed} {Elliptic-Hyperbolic} {Problems.}},
     journal = {Numerische Mathematik},
     pages = {259--272},
     publisher = {mathdoc},
     volume = {28},
     year = {1977},
     zbl = {0348.65097},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1977__28_132486/}
}