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Hurwitz proves the sharp universal square-root-five rational-approximation bound

Hurwitz proves that every real irrational alpha has infinitely many rational approximations p/q with |alpha−p/q|<1/(sqrt(5)q²). The constant sqrt(5) in the denominator cannot be uniformly increased: irrationals whose continued fractions are eventually all 1, including the golden ratio and its integral fractional-linear equivalents, obstruct every larger constant.

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Hurwitz proves that every real irrational alpha has infinitely many rational approximations p/q with |alpha−p/q|<1/(sqrt(5)q²). The constant sqrt(5) in the denominator cannot be uniformly increased: irrationals whose continued fractions are eventually all 1, including the golden ratio and its integral fractional-linear equivalents, obstruct every larger constant.

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Scientific scope

The universal quantifier is every real irrational, not every real including rationals and not a merely almost-everywhere statement. Infinitely many rational approximants have unbounded positive denominators; no finite precision search certifies the theorem. Sharpness is uniform over alpha, not a claim that every individual irrational has the same best approximation constant. Later refinements/Markoff classifications mentioned at the end are credited to Markoff rather than exported as wholly new Hurwitz theorems.

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People and systems

A. Hurwitz

Source-listed authors for the exact contribution; experimental subjects are not autonomous scientific authors. Source support and predecessor work retain separate roles. Individual effort shares and unresolved identities are not inferred.

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English catalogue narrative

Hurwitz proves the sharp universal square-root-five rational-approximation bound

Hurwitz proves that every real irrational alpha has infinitely many rational approximations p/q with |alpha−p/q|<1/(sqrt(5)q²). The constant sqrt(5) in the denominator cannot be uniformly increased: irrationals whose continued fractions are eventually all 1, including the golden ratio and its integral fractional-linear equivalents, obstruct every larger constant.

Scientific scope

The universal quantifier is every real irrational, not every real including rationals and not a merely almost-everywhere statement. Infinitely many rational approximants have unbounded positive denominators; no finite precision search certifies the theorem. Sharpness is uniform over alpha, not a claim that every individual irrational has the same best approximation constant. Later refinements/Markoff classifications mentioned at the end are credited to Markoff rather than exported as wholly new Hurwitz theorems.

Reading status

This is a source-linked WRS catalogue note. A full explanatory guide and independent scientific reconstruction have not been completed for this entry. Read the identified original work for its complete narrative and arguments.

People and systems

A. Hurwitz

Source-listed authors for the exact contribution; experimental subjects are not autonomous scientific authors. Source support and predecessor work retain separate roles. Individual effort shares and unresolved identities are not inferred.

Original sources