DAX for checking the combinations

Hello all,

i have following situation:

I could solve this in SQL with cross apply and for XML path command but looking for a way to do this now in DAX. I think "Distinct Client" and "Count PK" would be easy to implement with SUMMARIZE but how can i get a compilation of the contracts? In some cases i have over 250 same contracts and i need it just once in the column "Existing Contract".

Best Regards

Pikachu-Power