Arestov's theorems on Bernstein's inequality

We give a simple, elementary, and at least partially new proof of Arestov's famous extension of Bernstein's inequality in $L_p$ to all $p \geq 0$. Our crucial observation is that Boyd's approach to prove Mahler's inequality for algebraic polynomials $P_n \in {\mathcal P}_n^c$ can be extended to all trigonometric polynomials $T_n \in {\mathcal T}_n^c$.