A remark on a theorem of J. Tits

Let G be a rank two Chevalley group and F be the corresponding Moufang polygon. J. Tits proved that G is the universal completion of the amalgam formed by three subgroups of G: the stabilizer P₁ of a point a of F, the stabilizer P₂ of a line l incident with a, and the stabilizer N of an apartment A passing through a and l. We prove a slightly stronger result, in which the exact structure of N is not required. Our result can be used in conjunction with the "weak BN-pair" theorem of Delgado and Stellmacher in order to identify subgroups of finite groups generated by minimal parabolics.