3.3.3 Fixnums and flonums

A fixnum is an exact integer object that lies within a certain implementation–dependent subrange of the exact integer objects. Fixnums

Likewise, every implementation must designate a subset of its inexact real number objects as flonums, and to convert certain external representations into flonums. Flonums

Note that this does not imply that an implementation must use floating–point representations.