2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/218760We show that the plane Cremona group over a field of characteristic p > 0 does not contain elements of order of power of p larger than 2 and it does not contain elements of order p^2 unless p =2. Also we describe conjugacy classes of elements of order 4.10 pages,minor corrections, to appear in Proc. Steklov Inst. of Math., v. 264, 2009, 1--8Algebraic GeometryGroup Theory14E07text