Lemma. Refining feedback separates at least as many responses [ftip-00AG]

Let \(\mathcal Y\) be finite and let \(r_1:\mathcal Y\to \mathcal R_1\) and \(r_2:\mathcal Y\to \mathcal R_2\). Say that \(r_2\) refines \(r_1\) when

\[ r_2(y)=r_2(y')\quad \Longrightarrow \quad r_1(y)=r_1(y') \qquad (y,y'\in \mathcal Y). \]

If \(r_2\) refines \(r_1\), then

\[ \left |\mathcal Y/{\sim _{r_2}}\right | \geq \left |\mathcal Y/{\sim _{r_1}}\right |. \]

This finite lemma compares observational partitions only. It does not say that the refined reward is cheaper, more accurate, or better aligned with utility.