flet

(flet ((name lambda-list body...)...) body...)

Binds local functions for the body. Lisp-2: each name lives in the function namespace only, so it is reached from call position ((name args...)) and via #'name, while a bare name remains a variable reference. The definitions are NOT visible to each other or to themselves -- a definition body sees the outer function of the same name (use labels for recursion). Lambda lists support the same extensions as defun (&optional/&rest/&key/&aux).

Expands into let-bound lambdas plus a body rewrite, so a local function is an ordinary closure: it can capture surrounding variables and be passed to mapcar/funcall/apply via #'name.