Spectrum

:For other senses, including a variety of related meanings in the physical, mathematical, and biological sciences, see spectrum (disambiguation).

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In most modern usages of the word spectrum, there is a unifying theme of a variety of possible cases between extremes at either end. Older usages were not necessarily on that same unifying theme, but nonetheless led to the modern ones through a sequence of events set out below. Some modern usages in mathematics evolved out of that unifying theme but may be difficult to recognize as fitting into it.

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