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\begin{align}
 C_\mathrm{r} & = \eta_\mathrm{r} C_\mathrm{r}^\mathrm{crit} \\
 C_\mathrm{r}^\mathrm{crit} & = 2 \sqrt{I_\mathrm{r} k_\mathrm{r}} \\
 I_\mathrm{r} & = \left( \frac{1}{I_i + m_i r_i^2} + \frac{1}{I_j + m_j r_j^2} \right)^{-1}
\end{align}

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