The '''data processing inequality''' is an [[information theory|information theoretic]] concept whichthat states that the information content of a signal cannot be increased via a local physical operation. This can be expressed concisely as 'post-processing cannot increase information'.<ref name= BeaudryArxiv>{{citation |journal=Quantum Information & Computation |volume=12 |issue=5–6 |pages=432–441 |last1=Beaudry |first1=Normand |title=An intuitive proof of the data processing inequality |date=2012 |doi=10.26421/QIC12.5-6-4 |arxiv=1107.0740|bibcode=2011arXiv1107.0740B |s2cid=9531510 }}</ref>
