@article{NUMA_1981__37_132716,
     author = {R.A. Nicolaides and G.J. Fix and M.D. Gunzburger},
     title = {On {Mixed} {Finite} {Element} {Methods} for {First} {Order} {Elliptic} {Systems.}},
     journal = {Numerische Mathematik},
     pages = {29--48},
     publisher = {mathdoc},
     volume = {37},
     year = {1981},
     zbl = {0459.65072},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1981__37_132716/}
}