This work by Schumann, composed in 1894, was published with the solo part for either horn or cello.  Although a standard professional work, this piece tends to strike fear into the heart of many hornists.  The Adagio, a duo with piano and not a solo with accompaniment, has a high C (C6) approached by an octave slur, which is considered a difficult element.  Also challenging in this section is the control needed for the delicate piano entrances.  The Allegro section requires considerable endurance from even the most seasoned performer.  Additional sources of difficulty include the triplet with the slur-two, tongue-one articulation, the large interval slurs, and the sustained air support needed to play at the indicated forte and fortissimo dynamic markings for most of the movement.