Create two temporary tables with the same single integer column, and index only one of them. Insert the same 10,000 generated rows into each under EXPLAIN (ANALYZE). Keep all of it in answer.sql: temporary tables disappear when the session ends.
Expected: each plan shows 10,000 rows coming out of generate_series, and the insert into the indexed table takes longer. Timings move from run to run; run it twice if the gap is small.