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: properGroup.m
    path of file: ./repos/mtex/geometry/@symmetry
    
    the code of the file until where you have to start completion: function sP = properGroup(s)
% return the corresponding Laue group 

    
function sP = properGroup(s)
% return the corresponding Laue group 

if ~isempty(s.properRef)

  sP = s.properRef;

% if it is already a Laue group there is nothing to do
elseif s.isProper
  
  sP = s; 
  s.properRef = s; 
  
else

  % compute symmetry elements
  rot = s.rot;
  if s.isLaue
    rot = rot(~rot.i); % remove all improper rotations
  else
    rot.i = zeros(size(rot));   % make all rotations proper
  end