  We show that the linearity of an evolution of Quantum Mechanics follows from
the definition of kinematics. The same result is obtained for an arbitrary
theory with the state space that includes mixtures of different preparations.
Next, we formulate the non-signaling theorem and show that the theorem poses no
additional restriction on Quantum Mechanics provided the kinematics is given.
We also discuss validity of the postulate for the case of more general
theories.
