You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: restrict.m
    path of file: ./repos/chebfun/@spherefun
    
    the code of the file until where you have to start completion: function f = restrict(f, dom)
% RESTRICT  Restrict the domain of a SPHEREFUN.
%
% F = RESTRICT(F, DOM) is not supported for a spherefun F. A spherefun
% cannot be restricted. 

% Copyright 2017 by The University of Oxford and The Chebfun2 Developers.
% See http://www.chebfun.org/ for Chebfun2 information.


    
function f = restrict(f, dom)
% RESTRICT  Restrict the domain of a SPHEREFUN.
%
% F = RESTRICT(F, DOM) is not supported for a spherefun F. A spherefun
% cannot be restricted. 

% Copyright 2017 by The University of Oxford and The Chebfun2 Developers.
% See http://www.chebfun.org/ for Chebfun2 information.

error('CHEBFUN:SPHEREFUN:RESTRICT:fail',...
       'The domain of a spherefun cannot be restricted.')

end