Appel quickly distanced himself from the traditional artistic concepts of the art school and threw himself into experimentation with new forms. This is reflected in his early work, which was heavily influenced by the cubist visual language of Pablo Picasso (1881-1973). Appel and Corneille decided to travel to Liege in 1946 and their work was exhibited there a year later. The two also visited Paris, where Appel was impressed by the work of Jean Dubuffet (1901-1985), in which children and the mentally ill played important roles. Upon returning to the Netherlands, Appel came into contact, through Corneille, with the artist Constant (1920-2005). This trio exhibited in Amsterdam in 1948. Appel was constantly working on developing his own visual language, for which he drew a lot of inspiration from children’s drawings and primitive folk art. On 16 July 1948, Appel, Corneille and Constant founded the Experimentele Groep in Holland together with Anton Rooskens (1906-1976), Theo Wolvecamp (1925-1992), Jan Nieuwenhuijs (1922-1986) and Eugène Brands (1913-2002). The experimental poets Jan G. Elburg (1919-1992), Lucebert (1924-1994) and Gerrit Kouwenaar (1923-2014) joined later. The members of the Experimentele Groep in Holland made contact with similar groups from Denmark and Belgium. On 8 November of the same year, following a congress of surrealists in Paris, the Cobra art movement (1948-1951) was founded: an international movement of experimental working artists. Appel, Corneille and Constant were the co-founders together with Danish and Belgian artists.