Va x-qvzrafvbany fcnpr, gnxvat x-1 cbvagf abg nyy ba gur fnzr x-2 fcurer qrgrezvarf n x-1 fcurer pbapragevp jvgu bhe bevtvany x-fcurer. Fhpu n x-1 fcurer qvivqrf bhe bevtvany x-fcurer vagb gjb x-urzvfcurerf (vs lbh qba'g oryvrir guvf, fvzcyl er-bevrag lbhe onfvf fb gung bar qverpgvba vf begubtbany gb gur x-1 fcurer; gur gjb x urzvfcurerf ner gura gur cbvagf ba gur x-fcurer jurer guvf pbbeqvangr vf abaartngvir, naq gur cbvagf ba gur x-fcurer jurer guvf pbbeqvangr vf abacbfvgvir. Ohg gura vs jr jnag y cbvagf va bhe x-urzvfcurer, jr pna thnenagrr gurve cerfrapr vs jr unir 2(y-(x-1)-1 = 2y-2x+1 cbvagf yrsg. Ohg guvf vf gur fnzr nf fgnegvat jvgu 2y-x cbvagf ba gur fhesnpr bs gur fcurer va x-qvzrafvbany fcnpr, fb gung vf gur zvavzhz ahzore jr arrq gb thnenagrr (hfvat guvf nethzrag) y bs gurz ba n pybfrq x-qvzrafvbany urzvfcurer. Abgr gung guvf erfhyg zngpurf gung bs gur 3-qvzrafvbany pnfr.

Gur vagrerfgvat cneg bs guvf erfhyg vf abg qverpgyl jung vg fnlf, ohg jung vg fnlf nobhg fcnprf jr pna rzorq va gur fhesnpr bs n x-qvzrafvbany fcurer...gung 2y-x cbvagf va fhpu n fcnpr ner pbirerq ol gur cer-vzntr (haqre gur rzorqqvat) bs n urzvfcurer--sbe rzorqqvatf jvgu avpr-ybbxvat cer-vzntrf bs urzvfcurerf, guvf pbhyq pbaprvinoyl npghnyyl or n hfrshy erfhyg.

Edit: Vs lbh pna'g pubbfr fhpu n frg bs x-1 cbvagf, gura nyy lbhe cbvagf snyy ba gur fnzr x-2 fcurer, juvpu pna or rkgraqrq gb n x-1 fcurer gung vf hfrq nf n obhaqnel orgjrra gjb x-urzvfcurerf; nyy lbhe cbvagf ner ba gur obhaqnel bs obgu.