1 (define (make-frame dc origin edge1 edge2)
2   (list dc origin edge1 edge2))
3 (define (dc-frame f)
4   (car f))
5 (define (origin-frame f)
6   (cadr f))
7 (define (edge1-frame f)
8   (caddr f))
9 (define (edge2-frame f)
10   (cadddr f))