@article{AFM_1968_411-420_a2,
     author = {H. Lonka and O. Tammi},
     title = {On the use of step-functions in extremum problems of the class with bounded boundary rotation},
     journal = {Annales Fennici Mathematici},
     publisher = {mathdoc},
     volume = {411-420},
     year = {1968},
     doi = {10.5186/aasfm.1968.418},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1968.418/}
}