@article{10_4153_CJM_1990_033_x,
     author = {Hengartner, Walter and Szapiel, Wojciech},
     title = {Extremal {Problems} for the {Classes} {S} {R} -p and {T} {R} -p},
     journal = {Canadian journal of mathematics},
     pages = {619--645},
     year = {1990},
     volume = {42},
     number = {4},
     doi = {10.4153/CJM-1990-033-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CJM-1990-033-x/}
}