The art historian Douglas Cooper states that Paul Gauguin and Paul Cézanne "were particularly influential to the formation of Cubism and especially important to the paintings of Picasso during 1906 and 1907". Cooper goes on to say: "The Demoiselles is generally referred to as the first Cubist picture. This is an exaggeration, for although it was a major first step towards Cubism it is not yet Cubist. The disruptive, expressionist element in it is even contrary to the spirit of Cubism, which looked at the world in a detached, realistic spirit. Nevertheless, the Demoiselles is the logical picture to take as the starting point for Cubism, because it marks the birth of a new pictorial idiom, because in it Picasso violently overturned established conventions and because all that followed grew out of it."
Is it true that the first Cubist picture is The Demoiselles? 
although it was a major first step towards Cubism it is not yet Cubist.