This process involves an initial condition where $inc$ represents the included transactions, here given as ${a}$, and $pot$, which aims to be a refined version of $inc$, potentially including more transactions that enhance the overall feerate.

To compute $pot$, the procedure starts with setting it equal to $inc$, which in this scenario is ${a}$. The next step involves evaluating other transactions not yet included or decided upon, referred to as $und$, for their potential addition to $pot$. These transactions are considered in descending order of their feerate, disregarding any network topology constraints that might influence their selection.

The evaluation process follows a simple yet effective rule: add a transaction from $und$ to $pot$ if it increases the overall feerate. Applying this rule, when considering transaction $b$, the highest feerate transaction available in $und$ but not in $pot$, adding it to $pot$ results in a more favorable set ${a,b}$ compared to just ${a}$. Therefore, $b$ becomes part of $pot$. However, when the same evaluation is applied to transaction $c$, the inclusion does not result in a better feerate than the existing combination of ${a,b}$. Consequently, $c$ is excluded from $pot$, finalizing $pot$ as ${a,b}$.

This methodology underscores the principle that $pot$ is a pure function of both $inc$ and another set, $exc$, which presumably contains transactions explicitly excluded from consideration. Through this calculated approach, only those transactions that contribute to an increasing feerate are selected, ensuring an optimized outcome based on the criteria provided.