= Right-angle free-streamline hodograph map
{title2=$e^{\pi w}=\left(\frac{q^2-1}{q^2+1}\right)^2$}
For an inviscid irrotational unit-speed layer turning through a right angle, the <complex potential of a two-dimensional potential flow> occupies the strip $0<\operatorname{Im}w<1$ and its complex velocity $q$ occupies a fourth-quadrant quarter disk. The maps $r=q^2$, $s=(r-1)/(r+1)$ and $s^2$ take this disk to the upper half-plane, sending upstream velocity one, corner stagnation zero, and downstream velocity $-i$ to $0,1,\infty$. The map $e^{\pi w}$ has the same normalization, proving the displayed relation.
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