// refined variable function delay line
math vf2 {
	realDomain t;
	t.min=0; t.max=10; t.delta=0.25;
	real delay = 1;   // user-specified time delay
	real u(t);        // the normal state variable
	real udelayed(t); // the delayed state variable 
	when (t=t.min) u=1;
	u:t = -udelayed;  
	udelayed = if (delay < t.delta) u else
	    ( if (t-t.min < delay) 0 else u(t-delay));
}