@article{ZNSL_2000_268_a4,
     author = {L. Yu. Kolotilina},
     title = {Optimally conditioned block $2\times2$ matrices},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {72--85},
     year = {2000},
     volume = {268},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2000_268_a4/}
}