Semicircle: An exact relation in the integer and fractional quantum Hall effectM. Hilke, D. Shahar, S. H. Song, D. C. Tsui, Y. H. Xie and M. ShayeganEurophys. Lett., 46 6 (1999) 775-779DOI: https://doi.org/10.1209/epl/i1999-00331-2