(Def (PiCalc)
  ////////////////////////////////////////////////////////////////
  // Approximation to _Pi based on Algorithm 2.2
  // page 48 of Borwein and Borwein, Pi and the AGM.
  ////////////////////////////////////////////////////////////////
  (Local p a1 b1 c1 a2 b2 c2 k old new answer)
  (WithMorePrecision 20
    (Setq a1 1.0)
    (Setq b1 (Sqrt 0.5))
    (Setq c1 b1)
    (Setq old 0.5)
    (Setq k 0)
    (While TRUE
      (Setq a2 (/ (+ a1 b1) 2))
      (Setq b2 (Sqrt (* a1 b1)))
      (Setq c2 (/ (^ c1 2) (* 4 a2)))
      (PrintLine (/ (* 2 (^ a2 2)) (- 1 old)))
      (Setq k (+ k 1))
      (Setq a1 a2)
      (Setq b1 b2)
      (Setq c1 c2)
      (Setq new (+ old (* (^ 2 k) (^ c1 2))))
      (If (= new old) (Break))
      (Setq old new))
    (Setq answer (/ (* 2 (^ a2 2)) (- 1 old))))
  (Setq answer (Float answer))
  (Return answer)
)