What ulster song did beethoven use in his first piano concerto?

Beethoven incorporated the Ulster song "The Girl I Left Behind Me" in the second movement of his Piano Concerto No. 1 in C major, Op. 15. This theme reflects the influence of folk melodies and showcases Beethoven's ability to blend classical forms with traditional music. The song adds a lyrical quality to the movement, enhancing the emotional depth of the concerto.