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: fast9.m
    path of file: ./repos/ORB-MATLAB
    
    the code of the file until where you have to start completion: %FAST9. perform an  FAST corner detection from your FAST-ER generated tree
%    [corners, scores] = FAST9.(image, threshold) performs the detection on the image
%    and returns the X coordinates in corners(:,1), the Y coordinares in corners(:,2) and
%    optionally, the scores in scores(:). The score is computed using binary search over 
%    all possible thresholds.
%
%    [corners, scores] = FAST9.(image, threshold, nonmax) performs the corner
%    detection and nonmaximal suppression if nonmax is not zero. 
%    
%     If yo
    
function c = is_a_corner(i, posx, posy, b)
	cb = i(posy, posx) + b;
	c_b = i(posy, posx) - b;
        if i(posy+3,posx+0) > cb 
         if i(posy+3,posx+1) > cb 
          if i(posy+2,posx+2) > cb 
           if i(posy+1,posx+3) > cb 
            if i(posy+0,posx+3) > cb 
             if i(posy+-1,posx+3) > cb 
              if i(posy+-2,posx+2) > cb 
               if i(posy+-3,posx+1) > cb 
                if i(posy+-3,posx+0) > cb 
                 c=1; return
                else
                 if i(posy+3,posx+-1) > cb 
                  c=1; return
                 else
                  c=0; return
                 end