Recursion in lambda in Elisp

I have the following Python code: ``` def sum_fibonacci(): '''Project Euler: 2 Sum of even-valued terms of Fibonacci sequence < 4 mil ''' def i(a, b, acc): if a >= 4000000: return acc if a % 2 == 0: return i(a + b, a, acc + a) else: return i(a + b, a, acc) return i(2, 1, 0) ``` I want to translate it to Emacs Lisp. In Higher-order functions in Elisp i was told not to use `defun` within `defun`, because it enables the function globally, so i wrote lambda instead. But i need to make lambda call itself recursively. My code is: ``` (defun sum-fibonacci () (let ((i (lambda (a b acc) (cond ((>= a 4000000) acc) ((evenp a) (funcall i (+ a b) a (+ a acc))) (t (funcall i (+ a b) a acc)))))) (funcall i 2 1 0))) ``` However the function `i` is called before it is assigned with `let`, and i get an error - `*** Eval error *** Symbol's value as variable is void: i` How do i do recursion in lambda in Elisp?