\[ s = \dot{x} + \alpha D^\nu x \] \[ u = -K \text{sgn}(s) \] \[ \dot{K} = \gamma |s| \] \[ \text{Fractional Derivative: } \quad D^\nu x = \frac{1}{\Gamma(1 - \nu)} \int_0^t \frac{\dot{x}(\tau)}{(t - \tau)^\nu} d\tau \]