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: diff.m
    path of file: ./repos/chebfun/@chebfun3
    
    the code of the file until where you have to start completion: function F = diff(F, k, dim)
%DIFF   Partial derivative of a CHEBFUN3.
%   DIFF(F) is the 1st derivative of F along the 1st input variable.
%
%   DIFF(F, K) is the K-th derivative of F along the 1st input variable.
%  
%   DIFF(F, K, DIM) is the K-th derivative of F along the dimension DIM.
%   DIM = 1 (default) returns the derivative in the 1st input variable.

    
function F = diff(F, k, dim)
%DIFF   Partial derivative of a CHEBFUN3.
%   DIFF(F) is the 1st derivative of F along the 1st input variable.
%
%   DIFF(F, K) is the K-th derivative of F along the 1st input variable.
%  
%   DIFF(F, K, DIM) is the K-th derivative of F along the dimension DIM.
%   DIM = 1 (default) returns the derivative in the 1st input variable.
%   DIM = 2 returns the derivative in the 2nd variable.
%   DIM = 3 returns the derivative in the 3rd variable.
%
%   DIFF(F, [K1 K2], [DIM1 DIM2]) means K1-th derivative of F in dimension
%   DIM1 and K2-th derivative in dimension DIM2. DIM1 and DIM2 can be 1, 2 
%   or 3 in any order.
%
%   DIFF(F, [K1 K2 K3]) is the K1-th partial derivative of F in the first 
%   variable, K2-th partial derivative of F in the second variable and 
%   K3-th partial derivative of F in the third variable. 
%   For example, DIFF(F, [1 2 3]) is d^6F/(dx d^2y d^3z).
%    
% See also CHEBFUN3/GRAD, CHEBFUN3/LAP, and CHEBFUN3/BIHARM.

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

% Empty check:
if ( isempty(F) )
    return
end