Formula to return string "WK 26 - 6.2.25 - 6.8.25

Formula to return string "WK 26 - 6.2.25 - 6.8.25

Here's what I've got but syntatic failure:

if(not(isnull(${Deals.GS_Due})),
   "Week " + Tostring(ceil(dayofyear(${Deals.GS_Due}) / 7)) + " - " + 
   Tostring(month(${Deals.GS_Due})) + "." + Tostring(day(${Deals.GS_Due})) + "." + Tostring(year(${Deals.GS_Due})) + " - " + 
   Tostring(month(Adddate(${Deals.GS_Due}; 7))) + "." + Tostring(day(Adddate(${Deals.GS_Due}, 7))) + "." + Tostring(year(Adddate(${Deals.GS_Due}; 7))),
   ""
)

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