```common lisp
(cl:in-package #:clump-binary-tree)

(setf (documentation 'left 'function)
      (format nil "Given a binary tree, return the left child of that tree.~@
                   If an object other than a binary tree is given,~@
                   then an error of type INVALID-BINARY-TREE is signaled."))

(setf (documentation 'right 'function)
      (format nil "Given a binary tree, return the right child of that tree.~@
                   If an object other than a binary tree is given,~@
                   then an error of type INVALID-BINARY-TREE is signaled."))
```

Add English documentation for function (SETF LEFT).
user
```common lisp
(cl:in-package #:clump-binary-tree)

(setf (documentation 'left 'function)
      (format nil "Given a binary tree, return the left child of that tree.~@
                   If an object other than a binary tree is given,~@
                   then an error of type INVALID-BINARY-TREE is signaled."))

(setf (documentation 'right 'function)
      (format nil "Given a binary tree, return the right child of that tree.~@
                   If an object other than a binary tree is given,~@
                   then an error of type INVALID-BINARY-TREE is signaled."))

(setf (documentation '(setf left) 'function)
      (format nil "Given two binary trees, NEW and TREE,~@
                   make NEW the new left child of TREE.~@
                   NEW may be a node or NIL.~@
                   If TREE is NIL an error of type,~@
                   INVALID-BINARY-TREE is signaled."))
```
assistant