head.setParent(this);
    public Trace (Trace[] edges, Trace[] depends, InputTraceNode head)     {	if (edges == null)	    this.edges = new Trace[0];	else 	    this.edges = edges;	this.head = head;	if (depends == null)	    this.depends = new Trace[0];	else 	    this.depends = depends;	len=-1;    }