Huber recently established a reflection principle for functions polyharmonic of order p, applicable when the function and its first p-1 derivatives with respect to x1 vanish on the hyperplane of reflection X1 = O. His theorem includes as special cases the classical principle of H. A. Schwarz for harmonic functions and the corresponding results of H. Poritsky and R. J. Duff in for biharmonics. Assuming that a poly¬harmonic function of order p, meeting the above conditions on its derivatives, has an analytic continuation across this hyperplane, a locally valid expansion for the function is obtained in terms of its Cauchy data on the hyperplane. From this expansion an alternate reflection principle of limited range is obtained which is shown to be reducible to the Schwarz, Duffin, Huber principles for p = 1, 2, 3, respectively, within their common range of validity. Results for the iterated Laplace Equation are used which closely parallel those recently discussed by the author in AFOSR TH 58-340 of April, 1958. The paper closes with a brief description of a corresponding heuristic approach to the reflection principle for the Helmholtz equation treated recently by Diaz and Ludford. These results are to be presented at the Cambridge Meeting of the AMS, August 26, 1958.
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