Diffeomorfismi birazionali del piano proiettivo reale

Abstract

We study real birational transformations of the real projective plane which are diffeomorphisms. It turns out that their degree must be congruent to 1 mod 4, and that they are generated by linear automorphisms and transformations of degree 5 centred at 3 pairs of conjugated imaginary points. Our approach is inspired by recent proofs of the classical theorem of Noether and Castelnuovo that use the Sarkisov program.