Minkowski's question mark function

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Minkowski's question mark function

Wikipedia

Etymology

Defined by Hermann Minkowski in 1904.

Proper noun

Minkowski's question mark function

1. (mathematics) A function, denoted ?(x), with unusual fractal properties, mapping quadratic irrational numbers to rational numbers on the unit interval, via an expression relating the continued fraction expansions of the quadratics to the binary expansions of the rationals.