Swedish singer's Bjorn Ulvaeus, 2nd right, and Anni-Frid Lyngstad, right, of the pop group ABBA, sign autographs as they arrive on the red carpet for the band's International anniversary party at the Tate Modern in central London, Monday, April 7, 2014. The event marks the launch of ABBA – The Official Photo Book, the first ever authorised photographic biography of the band. (Photo by Joel Ryan/Invision/AP Images)

ABBA marks 40 years since breakthrough

Members of the Swedish supergroup marked 40 years since their international breakthrough hit “Waterloo” on Monday with a party for hundreds …