Write an emacs/lisp program (Provide proof it works)

Write a function that replaces all the occurrences of a value in a list with something else. For example, if the first line in the function is

(defun replace (L z y)

then L should be a list, a the value to be searched for in the list, and b the value to replace it with.

Inside this function, define a lambda expression taking one parameter, let's call it c. In this lambda expression, compare the parameter to the parameter c with a, and if they are equal, return b. Otherwise, return c. Store this lambda expression in a variable.

Next, use mapcar and the variable containing the lambda expression to apply the anonymous function just described to all the elements of the list L. The result should be the same list where c is replaced with b.

Result example: (replace '(3 1 5 6 3 2 3) 3 9) 

(9 1 5 6 9 2 9)