Roofit Conditional Function

Hello all and thanks in advance

I am trying to build a model in roofit but I haven’t concluded yet. What I want to do is make a fitting
function with observables x and 3 parameters a,b,g but what I need to do is to say that:

if x<g f(x)=0
else f(x)=…

I haven’t yet concluded how this can be done. rooprodpdf with condition? I can see how to do it on root but
I would like to use roofit.

Thanks again, George