help on select - Mailing list pgsql-sql

I need your help.

I have a table called medidas, in this table i have some ocurrences that has id_medida(primary key) id_ponto (sec_key) and also datetime field as timestamp.

i would like to know from a set of idpontos, e.g. 10,11,23,24.... how can i get the most recent date that is common to all??

for example, if idponto das date 2011-02-03 but none of others have this date in the db i dont want this. i want one common for all..

thanks.