l² space, often denoted as $$l^2$$, is the set of all infinite sequences of complex or real numbers for which the series of their squares is convergent. This space is a specific type of Hilbert space that possesses a complete inner product structure, making it fundamental in various areas of analysis and applied mathematics, particularly in representing functions through orthonormal bases and Fourier series, as well as in wavelet theory and frame expansions.
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