conv}  \sum_{r>0} \int_{0 < t_0 < \dots < t_r: t_0 + \dots + t_r = 0} \partial_{(t_0)} \dots \partial_{(t_r)} F_k(0) \partial_{(t_0)} \dots \partial_{(t_r)} G_k(0)\ \frac{dt_0 \dots dt_{r-0}}{t_0 \dots t_r} = \int_0^0 