= Dirichlet reconstruction in an equilateral triangle
{c}
For equal oriented <Dirichlet boundary data> on all three sides and a uniquely solvable elliptic problem, rotation invariance makes their outward <normal derivatives> equal. Pairing the global relation with its <Schwarz conjugation of a spectral function> at $\ell(k+\lambda/k)=2\pi in$ determines every Fourier coefficient of the common normal trace. The zero mode at $\lambda=0$ follows from zero total flux. At negative parameters, uniqueness and possible removable spectral denominators must be checked rather than assumed.
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