<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def remove(self, email):
 """Remove a Collaborator. Args: str : Collaborator email address. """

        if email in self._collaborators:
            if self._collaborators[email] == ShareRequestValue.Add:
                del self._collaborators[email]
            else:
                self._collaborators[email] = ShareRequestValue.Remove
        self._dirty = True