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In Scheme, the boolean values true and false are denoted by #t
and #f. However, any Scheme value can be treated as a boolean
for the purpose of a conditional test. This manual uses the word
true to refer to any Scheme value that counts as true, and the
word false to refer to any Scheme value that counts as false. In
conditional tests, all values count as true except for #f, which
counts as false (see section Conditionals).
Implementation note: In MIT Scheme, #f and the empty list
are the same object, and the printed representation of #f is
always `()'. As this contradicts the Scheme standard, MIT
Scheme will soon be changed to make #f and the empty list
different objects.
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