[1]> '(a.b) (A.B) ; this is an atom whose name contains a dot. [2]> '(a . b) ; this is a dotted pair expressed using the infix dot operator . (A . B) [3]> '(a . nil) ; dotting an object with nil produces a list. (A) [4]> '(a . (b c)) ; every list is a dotted pair whose second element is a list. (A B C) [5]> '(a . (b . c)) ; not every dotted pair is a (true) list. (A B . C) [6]> (LENGTH '(a . (b c))) 3 [7]> (LENGTH '(a . (b . c))) *** - LENGTH: A true list must not end with C . . . [8]> (CONS 'a 'b) ; but every dotted pair is a CONS. (A . B) [9]> (FIRST '(a . (b . c))) A [10]> (REST '(a . (b . c))) (B . C) [11]> (REST '(a . b)) B [12]> (REST '(a b)) (B)