function cells = conwayrule(cells,x,y,sum1)

sum1(x,y) = cells(x,y-1) + cells(x,y+1) + ...
    cells(x-1, y) + cells(x+1,y) + ...
    cells(x-1,y-1) + cells(x-1,y+1) + ...
    cells(x+1,y-1) + cells(x+1,y+1) -8;
% The CA rule
cells = ((sum1==3) | (sum1==2 & (cells-1))) + 1;