elementary equivalence

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Periodical Cicada, Adult, Magicicada spp. Requires 17 years to complete development. Nymph splits its skin, and transforms into an adult. Feeds on sap of tree roots. Northern Illinois Brood. This brood is the largest emergence of cicadas anywhere

Why Do Some Cicadas Appear Only Every 17 Years?

Cathedrale St.Jean in Lyon, France has a 14th-century astronomical clock that shows religious feast days till the year 2019; Perpetual Calendar

Ten Days That Vanished: The Switch to the Gregorian Calendar

Drinking water is poured into a glass.

Water Fluoridation: Just the Facts

King Cobra snake in Malaysia. (reptile)

9 of the World’s Deadliest Snakes

Happy, smiling, flying pig

7 Everyday English Idioms and Where They Come From

Dancers at a Cinco de Mayo festival at the Mission District, San Francisco, California. (Photo dated 2019.) holidays

Is Cinco de Mayo Mexico's Independence Day?

Portrait of a mountain gorilla at a short distance. gorilla close up portrait.The mountain gorilla (Gorilla beringei beringei)

Falling Stars: 10 of the Most Famous Endangered Species

elementary equivalence

logic

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model theory

In metalogic: Ultrafilters, ultraproducts, and ultrapowers
One application of these theorems is in the introduction of nonstandard analysis, which was…
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