  A new derivation is given of Branson's factorization formula for the
conformally invariant operator on the sphere whose principal part is the k-th
power of the scalar Laplacian. The derivation deduces Branson's formula from
knowledge of the corresponding conformally invariant operator on Euclidean
space (the k-th power of the Euclidean Laplacian) via conjugation by the
stereographic projection mapping.
