... textbooks

PVI or FGDP, for example, explain spectral factorization. More concisely in PVI, more richly in FGDP.

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... name

Any fact this basic should be named in some earlier field of mathematics or theoretical physics. Admittedly, the concept exists on an infinite cartesian plane without a helix, but all my codes in a finite space involve the helix, and the helix concept led me to it.

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