Abstract
Let $\psi:N\toR_\ge0$ be an arbitrary function from the
positive integers to the non-negative reals. Consider the set $A$ of
real numbers $\alpha$ for which there are infinitely many reduced fractions
$a/q$ such that $|\alpha-a/q|\psi(q)/q$. If $\sum_q=1^ınfty
\psi(q)\phi(q)/q=ınfty$, we show that $A$ has full Lebesgue measure.
This answers a question of Duffin and Schaeffer. As a corollary, we also
establish a conjecture due to Catlin regarding non-reduced solutions to the
inequality $|- a/q|\psi(q)/q$, giving a refinement of Khinchin's
Theorem.
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