We prove two conjectures of J. Tits on the unipotent elements of semisimple algebraic groups defined over a field with positive characteristic.
Philippe Gille. "Unipotent subgroups of reductive groups in characteristic $p > 0$." Duke Math. J. 114 (2) 307 - 328, 15 August 2002. https://doi.org/10.1215/S0012-7094-02-11425-2