help with "delete joins"

create table foo (a int, b int, c int, d text);

create table bar (a int, b int, c int);

insert into foo values (1,2,3,'a');
insert into foo values (1,2,4,'A');
insert into foo values (4,5,6,'b');
insert into foo values (7,8,9,'c');
insert into foo values (10,11,12,'d');

insert into bar values (1,2,3);
insert into bar values (7,8,9);
insert into bar values (10,11,12);

what i want to do is:

delete * from foo where not (foo.a = bar.a and foo.b=bar.b and
foo.c=bar.c) ;

so i end up with

postgres=# select * from foo;
a | b | c | d
---+---+---+---
1 | 2 | 4 | A
4 | 5 | 6 | b
(2 rows)

but thats not valid sql, is there some way to accomplish this?

Robert Treat