Are you talking about "(a . b)" ? The dot is not an operator. The dot is just there to denote a "pair". Linked lists in lisp are formed with pairs. So "(a b c)"

Are you talking about "(a . b)" ? The dot is not an operator. The dot is just there to denote a "pair". Linked lists in lisp are formed with pairs. So "(a b c)" is just a shorthand notation for "(a . (b . (c . null))". To sum it up: it's just syntax.