Hallgeir Øgaard

Hi! I'm sorry I'm answering this nearly 2 years after your question. It's not so long since I learned this piece, which I played at my final exam in Bergen in 2008. When I was learning the notes for this sonata, I also did a little research on the piece. guilmant's (the user profile here, not the composer) is correct in his thoughts. This chorale, which Guilmant (the composer) uses for the final movement, is written by himself, and doesn't occur in any liturgical material. This is at least what I've been told by ceveral french organists.