Finally, it is a real pleasure to contribute to this volume dedicated to our dear teacher and

Latin American mathematicians.

1. Commutation between real interpolation and intersections. Our initial motivation here

was a problem raised in [6] : Is (Lp,Lrn Ls) 0 = (Lp,Lr) 0 n (LP,L s) 0 q? The easy answer is ,q ,q ' yes and in fact the following result holds ( cf. [11]).