Douady-Hubbard Potential

Hi
In the page:
http://linas.org/art-gallery/escape/ray.html
Linas wrote:
"The Douady-Hubbard potential is just

f = e^(-m log2) = 2^(-m)
....
Lets define the derivative w.r.t a complex variable c=x+iy in the usual fashion:

D = d/dc = (d/dx - id/dy)/2

"

I don't understand it.
Does it mean
D:=df/dc
?

Adam Majewski
.