problem 1 2 4 in common lisp

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+;;;; ;;;;;;;;
+;;;; Even Fibonacci numbers
+;;;; Problem 2
+;;;;
+;;;; Each new term in the Fibonacci sequence is generated by adding the previous two terms.
+;;;; By starting with 1 and 2, the first 10 terms will be:
+;;;; 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+;;;; By considering the terms in the Fibonacci sequence whose values do not exceed four million,
+;;;; find the sum of the even-valued terms.
+;;;; ;;;;;;;;
+
+(defun sum (xs)
+  (if (null xs)
+    0
+    (+ (car xs) (sum (cdr xs)))))
+
+(defun fib (x y)
+  (when (> x 4000000) (return-from fib ()))
+  (cons x (fib y (+ x y))))
+
+(defvar *fibs-below-4m* (fib 1 2))
+
+(setf *fibs-below-4m* (remove-if-not #'evenp *fibs-below-4m*))
+(print (sum *fibs-below-4m*))