Exercise 2.47.  Here are two possible constructors for frames:

(define (make-frame origin edge1 edge2)
  (list origin edge1 edge2))

(define (make-frame origin edge1 edge2)
  (cons origin (cons edge1 edge2)))

For each constructor supply the appropriate selectors to produce an 
implementation for frames.

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(define origin-frame car)
(define edge1-frame cadr)
(define edge2-frame caddr)

The others are the same except for:

(define edge2-frame cddr)