Quite amazing how far beyond a run-of-the-mill Einstein puzzle this is.
Vg frrzrq gung gur qrrcre yriryf erdhver gur ragver chmmyr gb or n frdhrapr bs jbeqf, fb vg qvq srry n gnq ovg thrff-naq-purpx ng gvzrf. Gurer ner nyfb fbzr nzovthvgvrf orpnhfr Ratyvfu nf n ynathntr vf xvaq bs n zrff (rk: “rvgure N be O” pbhyq or rkpyhfvir be abg). Fgvyy ernyyl vaperqvoyr gung fb znal chmmyrf pbhyq or bireynccrq bagb bar nabgure!