sympy/sympy — pull request #1131 by pernici (2012-03-16 23:54:28+00:00)
Title: Denesting in a class of radicals with depth 3 via biquadratic equation.

Radicals of the form `z = sqrt(a + b*sqrt(r))`
where `a, b, r` are linear combinations of square roots of positive rationals on the rationals,
with `a**2 - b**2*r > 0`, can be denested in a simple way by solving a biquadratic equation.