select c.cname
from   customers c
where  not exists (
         select e.eno
         from   employees e, zipcodes z
         where  z.city = 'Wichita' and e.zip = z.zip and 
                     not exists (
                                select x.ono
                                from   orders x
                                where  x.cno = c.cno and
                                x.eno = e.eno));

