> (define (newton-cooling t T)
   (* -0.07 (- T 20)))
> (ODE-solve newton-cooling '(0 100) #:x-max 100 #:step 10)
'((0 100)
  (10 44.)
  (20 27.2)
  (30 22.16)
  (40 20.648)
  (50 20.1944)
  (60 20.05832)
  (70 20.017496)
  (80 20.0052488)
  (90 20.00157464)
  (100 20.000472392))