@article{NUMA_1992__61_3_133626,
     author = {E. S\"uli and K.W. Morton and T. Murdoch},
     title = {Optimal error estimation for {Petrov-Galerkin} methods in two dimensions.},
     journal = {Numerische Mathematik},
     pages = {359--372},
     publisher = {mathdoc},
     volume = {61},
     number = {3},
     year = {1992},
     zbl = {0783.65077},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1992__61_3_133626/}
}