Can you help me ? e1 and o1 cannot be resolved to a variable

[codenemy]

In e1, e2, and o1 i have get this error " e1 cannot be resolved to a variable"

i'm using eclipse java

public static void sortTopLeft2BottomRight(List<MatOfPoint> points){
        // top-left to right-bottom sort
        Collections.sort(points, (e1, e2) -> {

            Point o1 = new Point(e1.get(0, 0));
            Point o2 = new Point(e2.get(0, 0));

            return o1.y > o2.y ? 1 : -1;
        });
    }

    public static void sortLeft2Right(List<MatOfPoint> points){
        // left to right sort
        Collections.sort(points, (e1, e2) -> {

            Point o1 = new Point(e1.get(0, 0));
            Point o2 = new Point(e2.get(0, 0));

            return o1.x > o2.x ? 1 : -1;
        });
    }