菜鸟的问题 恳求解决

private void btn_catchMe_Click(object sender, System.EventArgs e)
        {
            MessageBox.Show("抓到我了，算你聪明！","抓到了");
        }

        private void Form1_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
        {
            int border = 50;//这定义了什么            
            int x = e.X;
            int y = e.Y;
            int left = btn_catchMe.Left//这定义了什么
            int right = btn_catchMe.Right;
            int top = btn_catchMe.Top;
            int bottom = btn_catchMe.Bottom;
            /* 鼠标到按钮附近(20个象素) */
            if( x > left - border && x < right + border && y > top - border && y < bottom + border)//这是什么方法 看不懂
            {
                btn_catchMe.Top += (y > top ? -20 : 20);
                if(btn_catchMe.Top > Form1.ActiveForm.Size.Height || btn_catchMe.Bottom < 0)
                {
                    btn_catchMe.Top = Form1.ActiveForm.Size.Height/2;
                }
                btn_catchMe.Left += (x > left ? -20 : 20);
                if(btn_catchMe.Left > Form1.ActiveForm.Size.Width || btn_catchMe.Right < 0)
                {
                    btn_catchMe.Left = Form1.ActiveForm.Size.Width/2;
                }

            }
        }