Leading Oscillator

//@version=2
// from Ehlers, John F. - Cybernetic Analysis for Stocks and Futures
study(title="Leading Oscillator",overlay=false)
pr=hl2
l=input(1,title="Moment len")
a1=input(.25,title="alfa 1",step=0.01)
a2=input(.33,title="alfa 2",step=0.01)
le=2*pr+(a1-2)*pr[l]+(1-a1)*nz(le[1])
nl=a2*le+(1-a2)*nz(nl[1])
ema=.5*pr+.5*nz(ema[1])
dif=nl-ema
ll=2*dif-dif[2]
plot(dif, color=silver,histbase=0, linewidth=2,transp=40,style=columns,title="lead")
plot(ll,title="trigger",color=lime,linewidth=1,transp=0)