By October 1857, Wagner had begun the composition sketch of the first act. During November, however, he set five of Mathilde's poems to music known today as the "Wesendonck Lieder". This was an unusual move by Wagner, who almost never set to music poetic texts other than his own. Wagner described two of the songs – "Im Treibhaus" and "Träume" – as "Studies for Tristan und Isolde": "Träume" uses a motif that forms the love duet in act 2 of "Tristan", while "Im Treibhaus" introduces a theme that later became the prelude to act 3. But Wagner resolved to write "Tristan" only after he had secured a publishing deal with the Leipzig-based firm Breitkopf & Härtel, in January 1858. From this point on, Wagner finished each act and sent it off for engraving before he started on the next – a remarkable feat given the unprecedented length and complexity of the score.