how to write correctly this update ? - Mailing list pgsql-general

I have tried many ways to update a table  :

UPDATE  personnes T1 SET T1.nom_naiss=T1.nom FROM  personnes T2, 
personnes T3
WHERE  ....;


UPDATE  personnes T1 SET T1.nom_naiss=T1.nom FROM  personnes T1, 
personnes T2, personnes T3
WHERE ..;


In my case , where clause is : WHERE T1.id=T2.id_mere AND 
T2.id_pere=T3.id AND T1.nom != T3.nom;

Thanks.

PC