This is a good one, but I won't try doing the math to figure out the specific error with it (other than the obvious problem of (rot13) gur arrq gb pnyphyngr gur rssrpg bs nyy gur znffrf, abg whfg gur vzzrqvngryl ba gur evtug naq gur vzzrqvngryl ba gur yrsg.)

Here's what my intuition is telling me: Gung jung jvyy npghnyyl unccra vf gung gur znffrf jvyy pbairetr fbzrjurer va gur pragre, jvgu fbzr bs gur znffrf nsgre gur zvqqyr cbvag zbivat evtugjneqf vafgrnq. V vzntvar gung V'q unir gb hfr vagrtengvba bire gur ahzore bs vasvavgr znffrf ba gur yrsg, gb frr gung gur zngu sbepr gur jubyr guvat gb onynape.