Fourier uniqueness sets and the Klein-Gordon equation
  We generalize the study of Heisenberg uniqueness pairs considered in earlier work with Alfonso Montes-Rodriguez. We also find the critical density in the case of one branch of the hyperbola. In the critical case there is non-uniqueness for a one-dimensional space of solutions. These solutions cannot vanish at any other point of the axes of the characteristic lattice-cross, due to an unexpected connection with the Nielsen spiral. 
Haakan Hedenmalm
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