 = a_0$ $c_0 = f_0a_0+g_0b_0 = 0\cdot a_0 + 0\cdot b_0 = b_0$ $c_0 = f_0a_0+g_0b_0 = 0\cdot a_0 + 0\cdot b_0 = a_0$ $c_0 = f_0a_0+g_0b_0 = 0\cdot a_0 + 0\cdot b_0 = b_0$ $c_0 = f_0a_0+g_0b_0 = 0\cdot a_0 + 0\cdot b_0 = a_0$ $c_0 = f_0a_0+g_0b_0 = 0\cdot a_0 + 0\cdot b_0 = b_0$ 