```common lisp
(defpackage #:squares
  (:use #:cl)
  (:export #:sum-of-squares
           #:square-of-sums
           #:difference))

(in-package #:squares)
```

Rename square-of-sums to square-of-sum to match the tests
user
```common lisp
(defpackage #:squares
  (:use #:cl)
  (:export #:sum-of-squares
           #:square-of-sum
           #:difference))

(in-package #:squares)
```
assistant