lispdoc  results for rationalize 
(rationalize x)  Function: Converts any REAL to a RATIONAL. Floats are converted to a simple rational representation exploiting the assumption that floats are only accurate to their precision. RATIONALIZE (and also RATIONAL) preserve the invariant: (= x (float (rationalize x) x))

Mentioned in: CLtL2  12.6. Type Conversions and Component Extractions on Numbers CLtL2  4.8. Type Conversion Function HyperSpec  Function RATIONAL, RATIONALIZE  
rationals  
Mentioned in: HyperSpec  12.1.3.2 Rule of Canonical Representation for Rationals HyperSpec  12.1.5.3 Rule of Canonical Representation for Complex Rationals HyperSpec  12.1.5.3.1 Examples of Rule of Canonical Representation for Complex Rationals  
By Bill Moorier 