English
On the upper half-plane, the hyperbolic distance between z and w equals 2 times the inverse hyperbolic sine of the Euclidean distance between z and w, normalized by the imaginary parts.
Русский
Расстояние по гиперbolической метрике между z и w на верхней полуплоскости равно 2 раз arcsinh(расстояние в ℂ между z и w, нормированное по.imaginary части).
LaTeX
$$$dist(z,w) = 2\, \mathrm{arsinh}\left(\frac{dist(z,w)_{\mathbb{C}}}{2 \sqrt{z.im \cdot w.im}}\right)$$$
Lean4
theorem sinh_half_dist (z w : ℍ) : sinh (dist z w / 2) = dist (z : ℂ) w / (2 * √(z.im * w.im)) := by
rw [dist_eq, mul_div_cancel_left₀ (arsinh _) two_ne_zero, sinh_arsinh]