A symbol may have more than one encapsulation of the same type, but only the most recent one can be undone. Saves the current definition of symbol , and replaces it with a function which returns the result of evaluating the form, body . Type is an arbitrary lisp object which is the type of encapsulation. A list of the arguments to the function. The unencapsulated definition of the function.
Type is compared with eq .
Encapsulations of other types are left in place. Returns nil otherwise.