This appendix presents an abbreviated account of Sommerfeld’s original analyses using multiple-valued solutions of differential equations.
Corresponding to the two differential equations under consideration, Sommerfeld used two methods of approach. The first was published in a paper concerning the diffraction of a plane wave by a perfectly conducting half-plane, and the second was published in a paper dealing with the solution of Laplace’s equation defined on spaces bounded by one and two branch lines. Unfortunately, the function derived for two branch lines was not a solution of Laplace’s equation: Sommerfeld was incorrect in his analysis, as shall be shown.
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