TY - JOUR AU - H. Lonka AU - O. Tammi TI - On the use of step-functions in extremum problems of the class with bounded boundary rotation JO - Annales Fennici Mathematici PY - 1968 VL - 411-420 PB - mathdoc UR - http://geodesic.mathdoc.fr/articles/10.5186/aasfm.1968.418/ DO - 10.5186/aasfm.1968.418 LA - en ID - AFM_1968_411-420_a2 ER -