$\backslash$table$[[$CUSTOMERS$,$cid,cname,city,discount$],[,c001,$TipTop,Duluth,$10\mathrm{.}00],[,c002,$Basics,Dallas,$12\mathrm{.}00],[,c003,$Allied,Dallas,$8\mathrm{.}00],[,c004,$ACME,Duluth,$8\mathrm{.}00],[,c006,$ACME,Kyoto,$0\mathrm{.}00]]$

$\backslash$table$[[$PRODCCTS$,$pid,pname,city,quantity,price$],[,$p$01,$comb,Dallas,$111400,0\mathrm{.}50],[,$p$02,$brush,Newark,$203000,0\mathrm{.}50],[,$p$03,$razor,Duluth,$150600,1\mathrm{.}00],[,$p$04,$pen,Duluth,$125300,1\mathrm{.}00],[,$p$05,$pencil,Dallas,$221400,1\mathrm{.}00],[,$p$06,$folder,Dallas,$123100,2\mathrm{.}00],[,$p$07,$case,Newark,$100500,1\mathrm{.}00]]$

$\backslash$table$[[$AGENTS$,$aid,aname,city,percent$],[,$a$01,$Smith,New York,$6],[,$a$02,$Jones,Newark,$6],[,$a$03,$Brown,Tokyo,$7],[$a$04,$Gray,New York,$6,],[$a$05,$Otasi,Duluth,$5,],[,$a$06,$Smith,Dallas,$5]]$

$\backslash$table$[[$ORDERS$,$ordno,month,cid,aid,pid,qty$,$dollars$],[1011,$jan,$c001,a01,p01,1000,450\mathrm{.}00],[1012,$jan,$c001,a01,$p$01,1000,450\mathrm{.}00],[1019,$feb,$c001,a02,$p$02,400,180\mathrm{.}00],[1017,$feb,$c001,a06,$p$03,600,540\mathrm{.}00],[1018,$feb,$c001,a03,$p$04,600,540\mathrm{.}00],[1023,$mar,$c001,a04,$p$05,500,450\mathrm{.}00],[1022,$mar,$c001,a05,$p$06,400,720\mathrm{.}00],[1025,$apr,$c001,a05,p07,800,720\mathrm{.}00],[1013,$jan,$c002,a03,$p$03,1000,880\mathrm{.}00],[1026,$may,$\frac{c}{O}O2,a05,$p$03,800,704\mathrm{.}00],[1015,$jan,$c003,a03,$p$05,1200,1104\mathrm{.}00],[1014,$jan,$cO03,a03,$p$05,1200,1104\mathrm{.}00],[1021,$feb,c$004,a06,$p$01,1000,460\mathrm{.}00],[1016,$jan,$c006,a01,$p$01,1000,500\mathrm{.}00],[1020,$feb,$c006,a03,p07,600,600\mathrm{.}00],[1024,$mar,$c006,a06,$p$01,800,400\mathrm{.}00]]$Using Relational Algebra, Get pids of products not ordered by any customer living in a city whose $($city$)$ namebegins with the letter D$.$ How can we find cities with names beginning with the letter D$?$