How do you calculate r2 using the D statistic and allele frequencies?

From the "Example" section of the notes:

• The D statistic is given as $D = 0.04$.
• The calculated allele frequencies are:
  • $P(A1) = 0.7$
  • $P(A2) = 0.3$
  • $P(B1) = 0.8$
  • $P(B2) = 0.2$

The formula for $r^2$ is:

$$r^2 = \frac{D^2}{P(A1)P(A2)P(B1)P(B2)}$$

$$r^2 = \frac{(0.04)^2}{(0.7)(0.3)(0.8)(0.2)}$$ $$r^2 = \frac{0.0016}{(0.21)(0.16)}$$ $$r^2 = \frac{0.0016}{0.0336}$$ $$r^2 \approx 0.047619$$

Rounding to four decimal places:

$$r^2 \approx 0.0476$$