@utilities.arguments_not_none<EOL><INDENT>def alias_grade(self, grade_id, alias_id):<DEDENT>
raise errors.Unimplemented()<EOL>
Adds an ``Id`` to a ``Grade`` for the purpose of creating compatibility.

        The primary ``Id`` of the ``Grade`` is determined by the
        provider. The new ``Id`` performs as an alias to the primary
        ``Id``. If the alias is a pointer to another grade, it is
        reassigned to the given grade ``Id``.

        arg:    grade_id (osid.id.Id): the ``Id`` of a ``Grade``
        arg:    alias_id (osid.id.Id): the alias ``Id``
        raise:  AlreadyExists - ``alias_id`` is already assigned
        raise:  NotFound - ``grade_id`` not found
        raise:  NullArgument - ``grade_id`` or ``alias_id`` is ``null``
        raise:  OperationFailed - unable to complete request
        raise:  PermissionDenied - authorization failure
        *compliance: mandatory -- This method must be implemented.*