(do ((i 1 (1+ i))
     (p 3 (* 3 p)))
    ((> i 4)
     p)
  (format #t "3**~s is ~s\n" i p))

is not 789 

but 243:

scheme@(guile-user)> (do ((i 1 (1+ i))
     (p 3 (* 3 p)))
    ((> i 4)
     p)
  (format #t "3**~s is ~s\n" i p))
3**1 is 3
3**2 is 9
3**3 is 27
3**4 is 81
243

this is not important but have to be corrected

Damien