code: private void trace(char mod, int i, int j)
  	{
  		if(mod == '0' || i <= 0 || j <= 0)      {
  			B1 = i + 1;
  			B2 = j + 1;
  		}
  		if(mod == 's')  {
  			trace(trace[i - 1][j - 1], i - 1, j - 1);
  			rep();
  		}
  		else if(mod == 'D')     {
  			trace(trace[i - 1][j], i - 1, j);
  			del(1);
  		}
  		else if(mod == 'd')     {
  			trace(dtrace[i - 1][j], i - 1, j);
  			del(1);
  		}
  		else if(mod == 'E')     {
  			trace(trace[i][j - 1], i, j - 1);
  			ins(1);
  		}
  		else if(mod == 'e')     {
  			trace(etrace[i][j - 1], i, j - 1);
  			ins(1);
  		}
  	}
docs: trace-back, recorded in sapp, wrong method!