ALGO_IT(T)
ST=STX=LAST=NIL
CT=T
while(ct!=NIL || st!=NIL)do
	if(ct!=NIL)then
		ret=1
		st=push(st,ct)
		stx=push(stx,x)
		ct=ct->dx
	else
		x=top(stx); ct=top(st)
		if(last!=ct->sx && ct->sx!=NIL)then
			a=val
			sta=push(sta,a)
			pop(stx)
			x=a+x
			stx=push(stx,x)
			ct=ct->sx
		else
			if(ct->sx=NIL)then
				a=val
				x=a+x
				y=1
				ret=x*1*ct->key
				+ uscita
			else
				y=val
				ret=x*y*ct->key
				+ uscita e pop vari