Ex12 3

$\def\abs#1{|#1|}\def\i{\mathbf {i}}\def\ket#1{|{#1}\rangle}\def\bra#1{\langle{#1}|}\def\braket#1#2{\langle{#1}|{#2}\rangle}\def\tr{\mathord{\mbox{tr}}}\mathbf{Exercise\ 12.3}$

What effect does applying $P_{\frac{\pi}{4}}$ to each of the qubits in the Steane seven qubit encoding have?