  For iterated Ore extensions satisfying a polynomial identity we present an
elementary way of erasing derivations. As a consequence we recover some results
obtained by Haynal in "PI degree parity in q-skew polynomial rings" (J. Algebra
319, 2008, 4199-4221). We also prove, under mild assumptions on
$R_n=R[x_1;\si_1,\de_1]...[x_n;\si_n;\de_n]$ that the Ore extension
$R[x_1;\si_1]...[x_n;\si_n]$ exists and is PI if $R_n$ is PI.
