Section 3.1 - Variables, syntactic keywords, and regions
Section 3.3 - External Representations
No object satisfies more than one of the following predicates:
boolean? bytevector? char? eof-object? null? number? pair? port? procedure? string? symbol? vector?
and all predicates created by define-record-type.
These predicates define the types boolean, bytevector, character, the empty list object, eof-object, number, pair, port, procedure, string, symbol, vector, and all record types.
Although there is a separate boolean type, any Scheme value can be used as a boolean value for the purpose of a conditional test. As explained in section 6.3, all values count as true in such a test except for #f. This report uses the word “true” to refer to any Scheme value except #f, and the word “false” to refer to #f.