Exercise 3.67.  Modify the pairs procedure so that (pairs integers 
integers) will produce the stream of all pairs of integers (i,j) 
(without the condition i < j). Hint: You will need to mix in an 
additional stream.

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As before, we can divide the infinite rectangular table, this time into 
four parts:

(S₀,T₀), the upper left corner.
(S₀,T₁)..., the rest of the row.
(S₁,T₀)..., the rest of the column.
(S₁,T₁)..., the rest of the table down and to the right.

(define (all-pairs s t)
  (cons-stream
   (list (stream-car s) (stream-car t))
   (interleave-3
     (stream-map (lambda (x) (list (stream-car s) x))
                 (stream-cdr t))
     (stream-map (lambda (x) (list x (stream-car t)))
                 (stream-cdr s))
     (all-pairs (stream-cdr s) (stream-cdr t)))))

(define (interleave-3 s t u)
  (cons-stream (stream-car s)
               (interleave-3 t u (stream-cdr s))))