Question: Björn Ulvaeus was a part of a Swedish pop group, formed in Stockholm in 1972, as well as co-producer on the film "Mamma Mia!" with who?
Related documents: [0]  [DOC] ABBA (] ) were a Swedish pop group, formed in Stockholm in 1972 by members Agnetha Fältskog, Björn Ulvaeus, Benny Andersson, and Anni-Frid Lyngstad. They became one of the most commercially successful acts in the history of popular music, topping the charts worldwide from 1974 to 1982. ABBA won the Eurovision Song Contest 1974 at The Dome in Brighton, UK, giving Sweden its first triumph in the contest, and are the most successful group to have ever taken part in the competition. [END] 
[1]  [DOC] Björn Kristian Ulvaeus (] ) (born 25 April 1945; credited as Björn Ulvæus) is a Swedish songwriter, producer, a former member of the Swedish musical group ABBA (1972–1982), and co-composer of the musicals "Chess", "Kristina från Duvemåla", and "Mamma Mia!". He co-produced the film "Mamma Mia!" with fellow ABBA member and close friend Benny Andersson. [END] 
Answer: 
Benny Andersson
Benny Andersson