Implement 'char<?', 'char>?', 'char'<=?' and 'char>=?' in Scheme

[Katie Burke]

These should return #t if the relation holds, #f otherwise.
http://www.scheme.com/tspl4/objects.html#./objects:s201

(char<? #\a #\b)

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

(char>? #\a #\b)

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

(char<=? #\Z #\W)

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

(char>=? #\Z #\W)

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