An AI found the bug in my code

Checking my own arithmetic made me uneasy. A calculator that calculates wrong is worse than no calculator. So I asked a different AI to re-derive every function from the statute, as if it had never seen my code.

I had treated the earned-income tax credit cap as a fixed value per income band. The law actually tapers it: within each band the cap shrinks as income rises. Around a salary of ₩70.1M my number was off by ₩110,000.

I re-checked the rates too. Korea's national pension went up to 4.75% for 2026 and the minimum wage became ₩10,320. After updating them I cross-checked against four separately published figures: minimum monthly wage ₩2,156,880, health-insurance premium ceiling ₩9,183,480, long-term care at 0.9448%, pension premium ceiling ₩626,050. All four matched.

The funny part is the other AI got something wrong too. It gave the credit cap as three bands; the statute has four. We were wrong in different places, which is the only reason both passes were worth running.