Car and cdr

In computer programming, car ⁱ/kɑːr/ and cdr (ⁱ/ˈkʌdər/ or ⁱ/ˈkʊdər/) are primitive operations on cons cells (or "non-atomic S-expressions") introduced in the Lisp programming language. A cons cell is composed of two pointers; the car operation extracts the first pointer, and the cdr operation extracts the second.