procedure sub(arg1,arg2)
local i
if i := integer(arg1) - integer(arg2) then
if i >= 0 then return i else return symop("0","-",-i)
return {
(if arg2 == "0" then arg1) |
(if arg1 == arg2 then "0") |
symop(arg1,"-",arg2)
}
end