= Bottom-boundary harmonic measure of a strip
{title2=$\rho_{x+iy}(a)=\sin y/[2\pi(\cosh(a-x)-\cos y)]$}
For <planar Brownian motion> started at $x+iy$ in $0<y<\pi$, this is its unconditional exit density on the bottom boundary. Its mass is $1-y/\pi$; the remaining mass $y/\pi$ lies on the top boundary. The <conformal bijection> $z\mapsto e^z$, the <Poisson kernel for the upper half-plane> and the boundary <Jacobian determinant> derive the formula. Conditional bottom-boundary density requires division by its mass.
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