* `(pair? lst)` tests whether `lst` is a pair; if `lst` is a non-empty list, it will also pass this test; if `lst` fails this test, it may be because `lst` is the empty list, or because it's not a list or pair at all
* `(car lst)` extracts the first member of a pair / head of a list
* `(cdr lst)` extracts the second member of a pair / tail of a list
* `(pair? lst)` tests whether `lst` is a pair; if `lst` is a non-empty list, it will also pass this test; if `lst` fails this test, it may be because `lst` is the empty list, or because it's not a list or pair at all
* `(car lst)` extracts the first member of a pair / head of a list
* `(cdr lst)` extracts the second member of a pair / tail of a list