/*
Find snum and sname of suppliers who have 2 or more
     shipments to all projects in the city they live in.

select snum, sname
from supplier S
where
      { projects shipped 2 times to by S }
      contains
      { projects in S's city}

select snum, sname
from supplier S
where not exists
      { projects in S's city}
	  -
      { projects shipped 2 times to by S }
*/

select distinct sname
from supplier S
where not exists (select *
                  from proj
                  where jnum in (select jnum
                                 from proj
                                 where proj.city = S.city)
                  and jnum not in (select jnum
                                   from spj
                                   where spj.snum = S.snum
                                   group by jnum
                                   having count(*) >= 2))
order by snum
