Implement 'rationalize' in scheme

[Katie Burke]

rationalize should return the simplest rational number that differs from real1 by no more than real2. ( http://www.scheme.com/tspl4/objects.html#./objects:s117 )

This should return 1/3.

(rationalize 3/10 1/10)

Traceback (most recent call last):
File "stdin", line 1, col 2
RunTimeError: unbound variable 'rationalize'