lispdoc  results for gcd 
(gcd &rest integers)  Function: Return the greatest common divisor of the arguments, which must be integers. Gcd with no arguments is defined to be 0.

Mentioned in: CLtL2  1.2.3. Evaluation, Expansion, and Equivalence CLtL2  12.4. Arithmetic Operations CLtL2  4.5. Type Specifiers That Specialize HyperSpec  Function GCD  
By Bill Moorier 