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math.FA2026
A Balian-Low theorem for nilpotent Lie groups
Ulrik Enstad, Jordy Timo van Velthoven
We prove strict necessary density conditions for smooth coherent frames and Riesz sequences in the orbit of a connected, simply connected, nilpotent Lie group. This extends previou…
math.CA2026
On the Calderón sum formula for wavelet systems
Ulrik Enstad, Jordy Timo van Velthoven
We show that the Calderón sum formula for orthonormal wavelet bases holds for arbitrary dilation and translation matrices under a mild condition on the wavelet function. This parti…