ANSI Common Lisp 12 Numbers 12.1 Number Concepts 12.1.5 Complex Computations
22.214.171.124 Rule of Canonical Representation for Complex Rationals
If the result of any computation would be a complex
number whose real part is of type rational and whose imaginary
part is zero, the result is converted to the rational
which is the real part.
This rule does not apply to complex numbers whose parts
For example, #C(5 0) and 5 are not different objects in Common Lisp
(they are always the same under eql);
#C(5.0 0.0) and 5.0 are always different objects in Common Lisp (they are never the same under eql,
although they are the same under equalp and =).
126.96.36.199.1 Examples of Rule of Canonical Representation for Complex Rationals