CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="390"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "mathoverflow.net",cType: 'managed',cRay: '92b7e0a03b50f9e6',cH: 'W9Mb6QKwVW.MRjCmxSXQmf7zCMOUIbfeQXiZYgXw_6Y-1743843860-1.2.1.1-2cFfkAwzk4IgL2YyWIB0pySiOoLFfDCX7UjMFgjcs_2kbKUEwjMUSEx7K9H4_As2',cUPMDTk: "\/q\/3888?__cf_chl_tk=2RlyPnACj7tcayECyQ7MBahkw.KjPht1fNTtY0nUTcE-1743843860-1.0.1.1-r68g0Z6oW9dVCjuofUUAq07aDLp3j615en6VngdZ_Js",cFPWv: 'g',cITimeS: '1743843860',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/q\/3888?__cf_chl_f_tk=2RlyPnACj7tcayECyQ7MBahkw.KjPht1fNTtY0nUTcE-1743843860-1.0.1.1-r68g0Z6oW9dVCjuofUUAq07aDLp3j615en6VngdZ_Js",md: "rEYeLINLAAdk5f2VXr6URVURJIO1kouSziQzyRXOI64-1743843860-1.2.1.1-A.0HqqW5uQRfkvsC7xpbHZTGkxq.d.fHkaeQjYPR3W84CXADS28NruTfovTUqNufaZCqbQtEQYELY7K.xVuD3TL.3q1s5O4V_QuR39NkrU8a8D._zXruWeVCvhEpVn7kjBy8W1.Ekyzy.f0y9ruOJdGUEZ1yA8Gt6_lLxIGbhXabmvwGInJOLGsHUjynUUu.Ha3BJLum2kdWnHjdREd4Hg6YDRUUXTtWHkzbpa7Cxg4pMns5cOKoMvkGQefyw4DTqGq.EQYs7NogR_d0xAR6sivcb26aJ3uZWNfWb1WPV_M6c6Ph2.uWp5BJ4qmLaCSN24Ipc7XEynOpqrppkHybCq.BfF.OaE6tVn3ijMg6r8JjicyibZ0ZFZXbVqaK85LAJHdovBVggmeD6aWQHV49jkqW7HmTpSLYcAlefoyskkSBCjXHBGBOKCsKthN0adRziLWBmCs9GyhhioQ.ElG26OyA4zrSMVmEeq7wbmdU2x2MsflgvP4G5XuWvrkbps2swYgXAlDhET7ymTrSyxP_vzjfAcWG3BBARpMRxKiDEbf11pOfdRzK3grOkDzwLavqRfU1u5raDGa.CSE_v5Ph13qoZbksLsonWOdZZ.YvFdbw_lTZkgq3RN6vJi95DmQIgpG6p0g8xnw0Sv03Xrnt.eScdpm7.fch.9WQKyL2IEla9yhHbVP35vmPlPJrGr4kolwMQy2VSIE7ByRqHoet89dDokl4K0VEoMqUaxt1a.d.MfXEw9fuFmTVxWRoKyOeDedPBSq3pIEj2vmP.NQ8kry6UmGOSb4ZPBNkpMr1Zr4xvnMSnaL1lEIEReL9tkgFiyJFR4enwkHp5DvQv3uSLDPyH_ZwgSNKShEwK7YFQhnRXKGTC7gnxifL.GPspOLTdNbqYhzAPZc_0nNmkl6tfTpuixKzPJMKa6.qpgGQfIDuRmJXdGpGRFGsoYNreZoGldqUbkTGxydx8WQZKll0R7dXEJTAcKSE_nGPoWmw0ImRPlJKXbI0PMsZ3xPjM4uxr1i7g4vOFMHQdCKUekOprWBEZJJdzFrJZbGCFnei.bzY.3Sd6i.mOnCjxt4Y5RcGTqvFQSwczZSXsv_G6T._G.uvdytch8umgfZugsg7OXCF5TxDFbYdTA1QOkMuo5j4C_XcaIhxuI.36UityL74tRyRNaiIVbCqfREgGwMh8KgAY80R69KSomvuF0_oTUkNUJqKiOMyxnjYFhdI7Uzq_g",mdrd: "IwGuqOYTp6yj_c3XC8lbXOCmpiUwkfmghsg5ipsuvHU-1743843860-1.2.1.1-ortirJs2_eiQdv_ourJCnUyL5QtJF7y5h4qql2W0eDsFh7UuXENl1jtFp2D1Xi0PaIrQDyseLoIFAKWxdwf50WHJ02SAAPn144GXSu9cnA4BnVB9GMOwwshIkAejolVwZM.muw_gSF9tk_k_wnsJ.qJa2snZwVUts2FHGSjLA4Qz10oNFxvj2xcfri.3IMtbCvJutY2JqgJySdLT2G6BdTGK6hQsNRjTk4E6rRrzlH47.Gg2azLCZlLdC0KGVyyGLpKsQXMohZl59ODmlq8auQB9KrvvBarivMLrnWesmo6KVSPZIym5jn6cBYJh6kTWWhHVtqMDhw5VOCAcQrJcX7pQBKhsLHyhIbQMAi5rgKixqi48bRnCbXjLH6fYL.F_lkTIDMV4Gc8oj6TyWndW.LLJvZHT1nvkMBdziTcv5ACPoi3FHte0_.77qwJOLmAGL6LabsG.fBNIjhse7N58lq.DfJ76_bB4am.4kSukuQUQi3qFvcpQaNC_J5zpnqOgmNprE0dCwtPvlX72FozmKDz..7rHW5jWPDWyoKFTFN7AOTUs9enT3IExxqkTzgNf6_WjnwBneVkjyoKs3FEAy5JO1m.wdfo7dCoX_v5n9TNuBjmPkbyM6RZiwN5V7qeEI_w9.OSHfUYWUR5Vc.fCq1VnriRnXsQ9RlKc_MksC60l7i6j0wbLRiLnnUzu7pQAQlBT_cvZNAJHdImYlS886mbR4pEityhJzQ3ZQBYlBETAJ8bGvBJqLKJazIcQyFHsZlkBazM7r7MOSkKPHXq7mdkhy_MBS8vmYJJzR1fvkHWbX9KZ1uAB5jp8DSi7YAUzIEB8iOVYdRDXiqdr1pXfgqliQFrPZg39x6aN7K0vlJzNR69.HrKDiIkOj7WXRmpibR9kXT8j7vkGWldfokcEKt7om5IxUyoGldwl2fcjj98TakP6.fnZ6sHfc..B9zER.vVKNijBmA7viQtXAHXI2Aonz89tBRGGqUGbkNXC6U1TTFV.oSyin4iufVYuCHnw6qUE311a1gj2ZEg1BvmeV3usdMvVQz0EHkzaE9DL_iv5zV19k4YjSrZPfatETIqPnisdrM1ch6OEPhxGz5NLVbcM7ARrXSbKnhhUwfOFFmbCwcgeEnNiZP0E5IochjvUWMa0pujsRu7.uF7M6IFL.xfhRxwj5ogxr88QnL.QIEPri9hqUMopvea7ExLKlr9k2p9LjnRH8mEAHj2uwVx8Bb.q4T5G8JsodQj4ab2lqTtEYunQ6sUc5ye750eSUYAWjhkcuC7jzwVGzpzCed3kFqgGYLzex987bt5x59mkr97h50DrWGR5xrNjT7uMzRur8XeJ9gcLcxSrU1bW8i2H4.KSVHSU3s2LCFUYjiMBZinvyqnUeA4FILPkjGiyv6W95Ksc1YVKAS3YzBjF1VimC3RUHQTUTCgSBxc_AWBTgm_qvAVRvHeTwnxQpR2FLVUpyZuQBm8VygXhXauPPX6uaLfh.Ce7YgyOH.e_a5tmbfZJqbTTg55rhEVDYg3nOsM3EFfZ_OO59peoiLJqpOAu2cloy1rEo0UzB1if3ZqlSP4fUgfTx3oucQnnxdc9J9wYQ.as2DEl_q6WmBO99RMvHIlEmsp_BEf2EzyoO21QDaCoRCtDMRfPYMi6g0oylVqBbKyiYFcYrKir8iZ6jfZTFt_GxZdnapTi_PRspyGfGBtC5cPCB68s47ofD36rLjxLldi6mf08UpqWa191xFX8bEBh8y37IYhXSheChKa98iwFee0zdQ0u0Q8i8pe21XJQyaXpiDBlHK0a7tYhoVXMg9wHWrYzGdQ0Qvsya.FjenckLAU0Kq.HKJ_iQvpNOFyPZPmynwQ2uUmRIcEG4r0eVlnOaWp67.tFbvBNPj8EmMDIsVSvF.KCxrrcWyOtiiKYyjSmJiQb9mfeSeqsxhHhRHAktvRMOkctdedyjKtxJJRZbm0W8pltXtxw_NwLvbBBXU3soy8YjskfOGDUgP1ZDj4P9dRbfzqs0u6G6IfLtqOBlLPgSvQvi0a_X8_7VqxvCgXoK5uRtYlf27Qyd2yAJg"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/g/orchestrate/chl_page/v1?ray=92b7e0a03b50f9e6';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/q\/3888?__cf_chl_rt_tk=2RlyPnACj7tcayECyQ7MBahkw.KjPht1fNTtY0nUTcE-1743843860-1.0.1.1-r68g0Z6oW9dVCjuofUUAq07aDLp3j615en6VngdZ_Js" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>