Question: What are the product ids for the problems reported by Christop Berge with closure authorised by Ashley Medhurst?
SQL: SELECT product_id FROM problems AS T1 JOIN staff AS T2 ON T1.reported_by_staff_id  =  T2.staff_id WHERE T2.staff_first_name  =  "Christop" AND T2.staff_last_name  =  "Berge" INTERSECT SELECT product_id FROM problems AS T1 JOIN staff AS T2 ON T1.closure_authorised_by_staff_id  =  T2.staff_id WHERE T2.staff_first_name  =  "Ashley" AND T2.staff_last_name  =  "Medhurst"