how would a unit root work for a linear process? why is unit root constant in mean in kpss test why does qt have a unit root? why does kpss not have a unit root why is the time series x_t$ non-stationary does kpss have a stationary process how does the term unit root relate to stationary process why does kpss have a unit root what makes a unit root nonstationary why does $x_t$ have unit roots? why does x_t$ have a unit root if a unit root is constant what is the relationship why x_t$ has a unit root is $x_t$ stationary how to explain unit root what is unit root of random walk why does the stationary test have a unit root what is unit root in kpss why does kpss.test have a unit root? how does unit root mean for random walks