Umbral

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Umbral is derived from the Latin word umbra, meaning "shadow". It is also the Spanish and Portuguese word for "threshold" and is sometimes used as a surname in those languages.

Umbral may also refer to:

• Umbral calculus, the surprising similarity between seemingly unrelated polynomial equations and certain shadowy techniques used to "prove" them
• Umbral moonshine, a mysterious connection between Niemeier lattices and Ramanujan's mock theta functions
• Francisco Umbral (1932–2007), Spanish journalist, novelist, biographer and essayist

• Umbra (disambiguation)

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