Singular invariant trilinear forms and covariant (bi-)differential operators under the conformal group

The residues of the meromorphic family of conformally invariant trilinear forms on the sphere (constructed in Clerc and Ørsted, in press, [2]) are computed. Their expression involves conformally covariant differential and bidifferential operators. For the latter, new formulæ are obtained. © 2012 Elsevier Inc. All rights reserved.