= Propeller domains
A propeller domain consists of seven congruent reflected triangles: one central triangle and three arms of two triangles each. There are different coloured gluing patterns whose <Dirichlet Laplacian> and <Neumann Laplacian> spectra agree by the <transplantation theorem>. Varying the three side lengths of a scalene triangle in a suitable open region gives three parameters; the central triangle is identifiable from the three reflex corners, allowing a direct nonisometry proof.
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