The vocal music of the so-called Franco-Flemish School developed in the southern part of the Low Countries and was an important contribution to Renaissance culture. Robert Wangermée and Philippe Mercier wrote in their encyclopedic book about the Walloon music that Liège, Cambrai and Hainaut played a leading part in the so-called Franco-Flemish School. Among them were Orlande de Lassus, Gilles Binchois, Guillaume Dufay In the 19th and 20th centuries, there was an emergence of major violinists, such as Henri Vieuxtemps, Eugène Ysaÿe (author of the unique opera in Walloon during the 20th century "Piére li houyeû" – Pierre the miner – based on a real incident which occurred in 1877 during a miners' strike in the Liège region), and Arthur Grumiaux, while Adolphe Sax (born in Dinant) invented the saxophone in 1846. The composer César Franck was born in Liège in 1822, Guillaume Lekeu in Verviers. More recently, André Souris (1899–1970) was associated with Surrealism. Zap Mama is a more international group. Henri Pousseur is generally regarded as a member of the Darmstadt School in the 1950s. Pousseur's music employs serialism, mobile forms, and aleatory, often mediating between or among seemingly irreconcilable styles, such as those of Schubert and Webern ("Votre Faust"), or Pousseur's own serial style and the protest song "We shall overcome" ("Couleurs croisées"). He was strongly linked to the social strikes in Liège during the 1960s. He worked also with the French writer Michel Butor. Walloon films are often characterized by social realism. It is perhaps the reason why the documentary "Misère au Borinage", and especially its co-director Henri Storck, is considered by Robert Stallaerts as the father of the Walloon cinema. He wrote: "Although a Fleming, he can be called the father of the Walloon cinema.". For F.André between "Misère au Borinage" and the films like those of the Dardenne brothers (since 1979), there is "Déjà s'envole la fleur maigre" (1960) (also shot in the Borinage), a film regarded as a point of reference in the history of the cinema.