#
Representation of line segments on the plane.
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Consider the problem of representing line segments in a plane. Each segment is represented as a pair of points: a starting point and an ending point. Define a constructor
`make-segment`

and selectors
`start-segment`

and
`end-segment`

that define the representation of segments in terms of points. Furthermore, a point can be represented as a pair of numbers: the
`x`

coordinate and the
`y`

coordinate. Accordingly, specify a constructor
`make-point`

and selectors
`x-point`

and
`y-point`

that define this representation. Finally, using your selectors and constructors, define a procedure
`midpoint-segment`

that takes a line segment as argument and returns its midpoint (the point whose coordinates are the average of the coordinates of the endpoints). To try your procedures, you'll need a way to print points:

```
(define (print-point p)
(newline)
(display "(")
(display (x-point p))
(display ",")
(display (y-point p))
(display ")"))
```