Roberto, ECJ doesn't have the equivalent of a .fn file, but it *does*  
have a few facilities that might be of use to you.
	1. ECJ can write out the expression in a syntax which, with a few  
tweaks, compiles as C.  See section of the ECJ Owner's Manual.
	2. The file ec/app/regression/convertToMathematica.lisp has a small  
lisp file which can convert ECJ's symbolic regression individuals into  
Mathematica expressions which are nicely graphed.

Sorry for the late response: I was away.


On Jun 8, 2011, at 9:31 AM, Roberto Oliveira Santos wrote:

> Hello,
> I'm running tutorial 4 and would like to generate a .fn file like  
> lil-gp, so
> I could plot a chart of my original function against the function  
> generated
> by my best individual.
> Kind regards,
> Roberto