= Solution
The <G-dwarf problem> is the observed shortage of metal-poor, long-lived disc <stars> relative to a simple <closed-box model of galactic chemical evolution>. In the fully evolved comparison, the half-rate <proportional-infall model of galactic chemical evolution> lowers the low-$Z$ fraction from $1-e^{-Z/y}$ to $Z/(2y)$, and prevents the closed-box tail from extending to arbitrarily high <stellar metallicity>. It therefore reduces the relative weight of the earliest metal-poor generation and the very metal-rich tail.
\b[This particular constant-proportional-infall model is an improvement, not a complete fit.] It still forms a metal-poor population immediately from its initially pristine reservoir, with nonzero constant $dN/dZ$ all the way down to zero, and predicts a broad linear distribution followed by an abrupt upper cutoff instead of a generally smooth, concentrated observed distribution. Comparison with observed abundance histograms must first use the same coordinate: its <logarithmic metallicity distribution> rises in proportion to $Z$ up to that cutoff, rather than remaining flat in logarithmic bins. https://arxiv.org/abs/astro-ph/9510101[Local G-dwarf measurements] exhibit a prominent logarithmic-abundance peak and a paucity of low-abundance stars; translating iron abundances into total $Z$ also requires an abundance-ratio model. More realistic histories can vary the <galactic gas inflow> and <star formation rate>, allow recycling and delayed enrichment, and account for migration and selection of different <stellar populations>; simply tuning a constant <stellar yield> does not remove all these shape deficiencies.
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