Simplified Common Lisp reference
Symbol class: Mathematics, Arithmetics, Logic and Comparisons
Symbol type: function
eqobject1object2 => T or NIL
Argument description:
object1 first object
object2 second object

EQ function compares object identity. It works for symbols and identical objects. It is not suitable for comparing numbers - see EQL and =. Result is true if they are same, otherwise false.

(eq 'moo 'moo) => T
(eq 'moo 'foo) => NIL
(eq 1 1) => T
(eq 1 2) => NIL
(eq 1234567890123456789 1234567890123456789) => NIL
(eq (cons 1 2) (cons 1 2)) => NIL
(let ((x (cons 1 2))) (eq x x)) => T
Function indexFull documentation for eq (HyperSpec)