Substitutions with Vanishing Rotationally Invariant First Cohomology by Juan García Escudero

“…The rank of the rational first cohomology, in the tiling space formed by the closure of a translational orbit, equals the Euler totient function evaluated at 𝑁 if the underlying rotation group is 𝐙𝑁. …”
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A new class of infinite products, and Euler's totient by Geoffrey B. Campbell

“…The idea of a q-analogue for the Euler totient function is suggested.…”
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