(idea) by nobody really Tue Nov 04 2003 at 23:57:34
arcsin(z) is equal to i × ln(√(1 − z²) − z × i) since sin(φ) = -i × sinh(i × φ).

The arcsine is real for -1 ≤ x ≤ 1 only. Values are then between -π/2 and +π/2.
I like it!