Fix typo

contents/gc.qmd

@@ -354,7 +354,7 @@ If the effective fields @eq-gc-effective-em were replaced by the standard fields
 
 The guiding-center equations of motion @eq-gc-u-time-derivative and @eq-gc-X-time-derivative can be used to derive the guiding-center energy equation
 $$
-\frac{\mathrm{d}H_\text{gc}}{\mathrm{d}t} = \frac{\partial H_\text{gc}}{\partial t} + \dot{\mathbf{X}}\cdot\nabla H_\text{gc} + \dot{u}\frac{\partial H_\text{gc}}{\partial u} = e\frac{\partial\Phi^ast}{\partial t} -\frac{e}{c}\frac{\partial\mathbf{A}^\ast}{\partial t}\cdot\dot{\mathbf{X}}
+\frac{\mathrm{d}H_\text{gc}}{\mathrm{d}t} = \frac{\partial H_\text{gc}}{\partial t} + \dot{\mathbf{X}}\cdot\nabla H_\text{gc} + \dot{u}\frac{\partial H_\text{gc}}{\partial u} = e\frac{\partial\Phi^\ast}{\partial t} -\frac{e}{c}\frac{\partial\mathbf{A}^\ast}{\partial t}\cdot\dot{\mathbf{X}}
 $$ {#eq-gc-energy-time-derivative}
 which implies that the guiding-center energy $E_\text{gc}\equiv mu^2/2+e\Phi^\ast$ is a constant of the motion for time-independent fields.