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Allegro CL

ANSI Common Lisp   12 Numbers   12.1 Number Concepts   12.1.3 Rational Computations

### 12.1.3.2 Rule of Canonical Representation for Rationals

If any computation produces a result that is a mathematical ratio of two integers such that the denominator evenly divides the numerator, then the result is converted to the equivalent integer.

If the denominator does not evenly divide the numerator, the canonical representation of a rational number is as the ratio that numerator and that denominator, where the greatest common divisor of the numerator and denominator is one, and where the denominator is positive and greater than one.

When used as input (in the default syntax), the notation -0 always denotes the integer 0. A conforming implementation must not have a representation of "minus zero" for integers that is distinct from its representation of zero for integers. However, such a distinction is possible for floats; see the type float.