The Variations on Ein Madchen oder Weibchen from Mozart's Singspiel Die Zauberflote may have been written in connection with Beethoven's aforementioned trip to Berlin, and therefore possibly date from around the same time as the first two cello sonatas (they were published in September 1798). Even though he did not go as far in giving the instruments an equal footing as he did in his Op. 5 sonatas, it is clear that Beethoven used this set as a type of experimentation to formulate his ideas.