= Two-sided cluster set at an interior slit point
{title2=$u\to\pm2/\sqrt{21}\text{ as }z\to i/2$}
In the explicit slit map, right-side approach to $i/2$ gives the positive root, and left-side approach gives the negative root. The corresponding lower-half-plane <boundary> values are $\pm25/(2\sqrt{21})$, so the two unit-circle image values are distinct. Every other <conformal bijection> onto the disk differs by a <disk automorphism>, which extends bijectively to the unit <circle>. Thus a sequence approaching that slit point has exactly one or both of two <boundary> cluster values, according to which sides occur infinitely often.
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