In computational complexity theory, the complexity class **ELEMENTARY** of **elementary recursive functions** is the union of the classes in the exponential hierarchy.

The name was coined by László Kalmár, in the context of recursive functions and undecidability; most problems in it are far from elementary. Some natural recursive problems lie outside ELEMENTARY, and are thus NONELEMENTARY. Most notably, there are primitive recursive problems which are not in ELEMENTARY. We know

- LOWER-ELEMENTARY EXPTIME ELEMENTARY PR R

Whereas ELEMENTARY contains bounded applications of exponentiation (for example, ), PR allows more general hyper operators (for example, tetration) which are not contained in ELEMENTARY.

Read more about ELEMENTARY: Definition, Lower Elementary Recursive Functions, Basis For ELEMENTARY, Descriptive Characterization

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“Listen. We converse as we live—by repeating, by combining and recombining a few elements over and over again just as nature does when of *elementary* particles it builds a world.”

—William Gass (b. 1924)

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