  In this paper, we prove a maximum principle for the general multi-term
space-time-fractional transport equation and apply it for establishing
uniqueness of solution to an initial-boundary-value problem for this equation.
We also derive some comparison principles for solutions to the
initial-boundary-value problems with different problem data. Finally, we
present a maximum principle for the Cauchy problem for a time-fractional
transport equation on an unbounded domain.
