  The invariance of the Welschinger numbers for real unnodal Del Pezzo
surfaces, which we used for the enumeration of real rational curves on real
toric Del Pezzo surfaces (see math.AG/0303378 and IMRN 49 (2003), 2639-2653),
follows from J.-Y. Welschinger's theorem stated and proved in a symplectic
setting (math.AG/0303145 and CRAS, Ser. I, 336 (2003), 341-344). Here, we give
an algebraic geometry version of the proof of the above invariance.
