(One approach would be to repeatedly differentiate ∂ H / ∂ u {\displaystyle \partial H/\partial u} with respect to time until the control u again explicitly appears, which is guaranteed to happen eventually.
（有一個作法是重複的將 ∂ H / ∂ u {\displaystyle \partial H/\partial u} 對時間微分，直到有出現顯式控制項為止，之後可以令該式為0，求解u。