Past exam of the perturbation methods and applied complex variables course of the University of Oxford / 2010 / B / 4 / ii / Solution

Use the branch of $\sqrt{1-Z^2}$ that is positive for $Z=iY$, $Y>0$. The right-half-plane slit mapis holomorphic in the upper half-plane, with derivative $Z(1-Z^2{)}^{-3/2}$, the required Schwarz-Christoffel formula form. Its derivative has no interior zero.

To verify the image and global injectivity, factor the construction. Squaring maps the upper half-plane bijectively onto $\mathbb{C}\setminus [0,\infty )$. Thus $1-Z^2$ ranges over $\mathbb{C}\setminus (-\infty ,1]$. The positive-real-part square root maps this onto the right half-plane with the interval $(0,1]$ removed; reciprocation maps it onto the right half-plane slit along $[1,\infty )$. This also identifies the slit tip as a boundary point; the strict inequality in the printed slit description must be understood with that boundary convention.

Approaching the real axis from above givesIn particular $Z=-1$ maps to the lower infinite prime end $A$, $Z=0$ to the tip $B=1$, and $Z=1$ to the upper infinite prime end $C$. The real-axis point at infinity maps to zero on the vertical wall.