We establish a precise unitary equivalence between the circle Laplacian −π∂²θ on S¹ and a compactified version of the Berry-Keating operator −π (x∂x) ² on the interval [1, e²π) with measure dx/x. Both operators share the discrete spectrum πk²: k ∈ Z. The ϕ (n) -averaging operators, defined using coprime residue groups (Z/nZ) ×, translate between the two settings via the logarithmic coordinate transformation, providing a precise arithmetic characterisation of the operator domains
Trent Palelei (Sun,) studied this question.