Finding the Number of Rectangles

You are given a list of distinct (x, y) coordinates. Create a function that returns how many rectangles these points form on the plane.

Examples

rectangles([(1, 1), (2, 1), (1, 2), (2, 2)]) ➞ 1

rectangles([(1, 1), (2, 1), (1, 2), (2, 2), (3, 1), (3, 2)]) ➞ 3

rectangles([(1, 1), (1, 2), (2, 1), (2, 2), (3, 1), (3, 2), (3, 3), (2, 3), (1, 3)]) ➞ 10
# Note: We have a rectangle with vertices (2, 1), (3, 2), (2, 3), and (1, 2).

Notes

Don't forget to count rectangles that aren't parallel to the x- and y-axis (see example #3).