Kraft fathered a child to whom Copland later provided financial security, through a bequest from his estate. Vivian Perlis, who collaborated with Copland on his autobiography, writes: "Copland's method of composing was to write down fragments of musical ideas as they came to him. When he needed a piece, he would turn to these ideas (his 'gold nuggets')." if one or more of these nuggets looked promising, he would then write a piano sketch and eventually work on them at the keyboard. The piano, Perlis writes, "was so integral to his composing that it permeated his compositional style, not only in the frequent use in the instrument but in more subtle and complex ways". His habit of turning to the keyboard tended to embarrass Copland until he learned that Stravinsky also did so. Copland would not consider the specific instrumentation for a piece until it was complete and notated. Nor, according to Pollack, did he generally work in linear fashion, from beginning to end of a composition. Instead, he tended to compose whole sections in no particular order and surmise their eventual sequence after all those parts were complete, much like assembling a collage. Copland himself admitted, "I don't compose. I assemble materials." Many times, he included material he had written years earlier. If the situation dictated, as it did with his film scores, Copland could work quickly. Otherwise, he tended to write slowly whenever possible. Even with this deliberation, Copland considered composition, in his words, "the product of the emotions", which included "self-expression" and "self-discovery". While Copland's earliest musical inclinations as a teenager ran toward Chopin, Debussy, Verdi and the Russian composers, Copland's teacher and mentor Nadia Boulanger became his most important influence. Copland especially admired Boulanger's total grasp of all classical music, and he was encouraged to experiment and develop a "clarity of conception and elegance in proportion". Following her model, he studied all periods of classical music and all forms—from madrigals to symphonies. This breadth of vision led Copland to compose music for numerous settings—orchestra, opera, solo piano, small ensemble, art song, ballet, theater and film. Boulanger particularly emphasized "la grande ligne" (the long line), "a sense of forward motion ... the feeling for inevitability, for the creating of an entire piece that could be thought of as a functioning entity".