[GiNaC-list] substitute for step ( wild ( ) ) function derivative

[jros]

Hello,

If I derive step I obtain D[0](step). I want to substitute for
D[0](step)--> 0 to get a particular behavior.

What should I do?

(e.subs(D[0](step)(wild()) == 0) can't be understand

diff(step(wild()),wild()) neither.

Any clues.

By the way I'm assuming that the step function is the Heaviside function
( step(x)=0 if x<0; 1 otherwise I'm assuming a real argument) .

Thank you in advance.

Javier