import java.io.PrintStream;

 class BoxedList_double_3d_ {
    private List_double_3d_ l = null;

    public BoxedList_double_3d_() {
    }

    public BoxedList_double_3d_(double [3d] x) {
        push(x);
    }

    public void push(double [3d] item) {
        l = new List_double_3d_(item, l);
    }

    public double [3d] pop() {
        double [3d] t = l.first();
	l = l.rest();
	return t;
    }

    public double [3d] first() {
        return l.first();
    }

    public List_double_3d_ toList() {
        return l;
    }

    // Destructive append.
    public BoxedList_double_3d_ concat(BoxedList_double_3d_ x) {
      if (l == null)
	l = x.l;
      else if (x != null)
	l.concat(x.l);
      return this;
    }

    public double [1d] [3d] toArray() {
	double [1d] [3d] a = new double [[0 : length() - 1]] [3d];
	int i = 0;
	for (List_double_3d_ r = l; r != null; r = r.rest()) {
	    a[i] = r.first();
	    i++;
	}
	return a;
    }

    public double [1d] [3d] toReversedArray() {
	int i = length();
	double [1d] [3d] a = new double [[0 : i - 1]] [3d];
	for (List_double_3d_ r = l; r != null; r = r.rest()) {
	    a[--i] = r.first();
	}
	return a;
    }

    public boolean isEmpty() {
	return l == null;
    }

    public int length() {
	return l == null ? 0 : l.length();
    }
}