atom object ⇒  generalized-boolean
| object | an object. | 
| generalized-boolean | a generalized boolean. | 
 (atom 'sss) ⇒  true
 (atom (cons 1 2)) ⇒  false
 (atom nil) ⇒  true
 (atom '()) ⇒  true
 (atom 3) ⇒  true
 (atom object) ≡ (typep object 'atom) ≡ (not (consp object))
 ≡ (not (typep object 'cons)) ≡ (typep object '(not cons))