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: "zbmath.org",cType: 'managed',cRay: '92ed0fa59fc7a060',cH: 'AvIxCTqgcyaG7sS0wtiEiJmPN1ROMsV1oP6BttnLPWM-1744401531-1.2.1.1-v1xYC1jBU5c3GUgztvTiIJE7Q9TmVZoVVE_xk9L8vU81eWnPSjZRdle5sN5gbZAV',cUPMDTk: "\/authors\/shu.zhan?__cf_chl_tk=_bke1x2zyA6BDz.5gijze.I4QMkF_03xBIYn7Of2Lkg-1744401531-1.0.1.1-nfzmHzajyAU12DBqd2equqlYP3PMtiXMJ9JtnhV9F4c",cFPWv: 'b',cITimeS: '1744401531',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "unsupported_browser_beacon",fa: "\/authors\/shu.zhan?__cf_chl_f_tk=_bke1x2zyA6BDz.5gijze.I4QMkF_03xBIYn7Of2Lkg-1744401531-1.0.1.1-nfzmHzajyAU12DBqd2equqlYP3PMtiXMJ9JtnhV9F4c",md: "CnuLes3KUEsbWKbJliK6emu0lXfBVEJqhs_2Jk8iZ1o-1744401531-1.2.1.1-wAZ5RlFtG8cv1eyMCrUANAlb6ni8IUD5RSnWgZ2XI5zK5bo14AJUvKBYT.mRZzCDAXQbzld0aGdk50c4V9DQK.oa1VyeAlXUsU3QUaTf9.HqE8BAQdGz4NMTfKullgPGAurKkB0gVfOrvq4i_q3iLOpClYvsIjgdNj0ufCEDoRvc2ZIrC6j.j6WJ6HLmW8i7kCVtTMDhR8szB3yhrE6xyLhXz_4yBHqP.96meDMr2anqz9CPOumPoYR0qJ2LKFQWs0Q_cCvKLPRSosbULgPuQC1D9pMH123HRD_UxSqshuO1rDLLuDSHsAizb8bGW9T70HkScnulof6sMsmdJLPU7miLx_gMBCHrnw3zCZTjvR6nlnS8.XDsuq.Epk_N0OCFTwWLpNSEgU6VFAZN.JVrA4Zwv8eKHN.BuE8uVPTExotqcEncHxyFgkFI75lr3p8eEoJjxdG7NI9Rmabi_IKaSuONRoLSzGig.kpCVTayTbPz.TMn7sUH_ebaE72gyMBvKlX4wpBgkYUanMiLi6vCI5hTxRGgJ3WLjUX1K6ozYOAeo6LMbbW1eUJnjcAwzK7BzA52z.nHPzm_dujijtQJrTwar4uLvwpxZzRYlNXpeExXZAgKXePtKB0gW2gmJvM.TV2OJ4z8pv11z1xu35ubNJF_3uJ2ay4b.oBalsMXoD8m7EDjCWst.Jqjvd3Z8.dcE27Mo.W34pmM2mvSu1NlT4WLEr_vMkucakaX9GiajutxP4jWiHqGaZOiMLwo_cIz0A8XsvZuUGIAlTFNnadVBL6d2YpzT2yMDUhvNS._xzo1LKI2._9qsT70KLCbzLvu6syfJkB8_OK86JAqhwYB7Os97p4FCbBL1djUIjc2qWwUy3cgqqSkfuly0337tkm6BAZNNKCzQP.SO8N7dh0MO87ZtyGT0emXpmrHXDShuaotUHNewGTFJIKSmrSEgqF2cAQW3rcPO_WYxrUyGzQBz79u5QfjvoDqyOiqZzcjPTiYNSdMKJzTAl__G.FnxIhlJdZK1ozz398MUXOG0okqtiVpb19v19Wi4LRBkU_uH6iJIIdPk1v8WQYZom36N8gHXRs4mrIGfdRl86MXoZwW_3uDKwvEakjYUhGpbvGbxYJXZw2U7ejNjEpP4btD8ueYCswuQv7RqTqcL0q6x8fDW2KKDnG.qVcmgvZhm8Njl0ylgNdf4B3jEIHK_AJqa8cMTGPm5.ZnAiMZTzWzSD.Rvw",mdrd: "VVsMs3FE.qI552c2hgx5GMxQZBspGMFzS4mKoWNAxPI-1744401531-1.2.1.1-RAROiU58GOalBgyOM_xlD8aAniIC.h6t2g91rtfBY3leu5i0IIGaa9HEJdX1EO.GdGx9zBBjabFa.rKzxCTUBwIXSEKbCIhiVH4LStHgcjsxbaQsSgrN7n2iIHp4en_6a2vzlTtlunCbBCQXC7ulKP9fsbYKgtOfefNfV5i0vEuDMSrePjaVRJo_WOXyyXmU10sRA5FsUt4DFlolUkMd5jAtFM1ImbA9rVR1ON.xtzrYbxVj2i5ByHOmXP7HTErEHrn5Fuy5YlsxLiJEWVDKC4zeDH3rKeimuTqY.XRhoP_1eNPIdn8p3kPRc2ag1Ly_g0JNcK6H0LnmUa3.H.UsWaiSkdkg2KadJavyKiXrFnN.DLe66l892HTq903yyVuO.CsKguJt9a.QqTMNd5E9b6QkVryuufEcT0jHvUQkGBd_5_svM10gFyQhCH7_w_PEYsDrmFg61a_CK9lA0xSJLO_TUrrAX2arzdTYP_Lh00vfqa_VFob.9dO0KkXjn6Sgve4FuVRCuaDdpWek.WBE18KxCRid5iPgVCeunZiwGPJOHuF8NcRSGoNzui.Ho_MLX.m8FsjAZ3ti_SlaZBSI.enwHhlWLzVoRvPAyotFeq7_P9oMxDegqM5YqeFk2vvt0DH0cnRTr_QUeSa503H89TarEUoD4zeEpN4QxC6zb3m.ecwSM2tDVUajO9zzYHWGlSVacAyk3hMJy95ufZ.mhWP2LegSKNEUbV9AuQfrAjtyNyxK38Db7c8EpkkbNujkdmiXxOdqigd3Ag7o5_XJ43txK2.tWO3UTuAqOz1wTgeXu09k0g0MHR0oawHx9orzX8H9wQXJIjqKudQq9of7eHRaq4pz2bQ31f_SAaOSXx9qiCJ_sqEIPIxXF8fApdSRCE79livl283WT2glw21OkSy6D_c3m7f_oxBk1VSn47Qw52KHhIPKw0kqalU6Bnwfif0MtYZK90rSO6rfLCAC4p8us8Ek5wlrKmoycJudKaR4wL48yEEt8cuqxKasapRNbc.5vrTjb4itEaD0l3bORB_hl1ZHlBlBEF9_0VRS3JonoZQWrXhr0.Q517vu7k5HGye9BXB1u94A4vAWGj639uJgge.3umyggnQHJUObUjPeJZZN30Y16PMI0rP7Ebb9CVuUmUHowlQOJLEBHQSr4WtOXqQm2ihDoP6kXRv6.R0cz1ml5MRxLYy9dOSA2mqR4IE957LG_x3bTqhRusE62yUREkebJq4kEC6LdOxDZ2O7QY6sE8hzmEs_oHjAuzNOJKPHEIacJpQCtBPtBpAmjAo7k3vg9zyxgjm41BNBbHN21KxaAr.XUaYOXZrekRLVosx8XqpM3g9HwLmF6uq9r_mJca1ZNiK.mEOVlFKjWMawDt0zqNV_G30CV5OAZwWKYNdagXCh1XSeWNisFvxtEO8OaO3jqMIFg3LxDKV1SSZg3Z9HegQ00LhjDyaLRaUPewbEPhumX5IkploJ97w0OR1PU1KASVbU8yFDggu_ZvWdB4HDRLXySJMZhriWX34s_whOEwMvBDjrnrtf3EcV2mr.F4j9Md9mcrkal8c6dmSusC264vrqFptTIswOCiAYeMXomjtiFLpFqE6LQcJ2lc6SXA6CgDQ2cukW1bag9znnb44Pbcz9L8KKSHy0h7DmEjCC89_ILKrI9mjKjlZyX5e46.YQecrrBVyxvDrL2yo..oXXz_sDHOyH4Ys.K.3CAhliPaoqienU1vgzpsgtWmMI9ND9Raxr9.Q8NnUknfxR_TvK7EYFS3GR1IX_6Y1bXHRPvK2F7D1Xy89PGpIJZhXFjEPARw3GJpVwYpDVYfhZouj9_wrKYTl0hlqWh9kT1SRY9CW1ZbPiNK2JAz.cXqYyXzQi0WZ.uoI7zpTV1kyM48aXyAjsXiXZkYiv7t7mfH0L1joSwR_kiipx58PMaqyX9iC7jmqd3Zrc1eaImSnLv9cbVFfUsqPx6jkcTNADD9yBREoxTHrSW6MyQ_3SE.FrRQfmS_9NGPODkVdZ5xRYBq6PusfrLIbZ2SLunhOHAiSjXCEmrEcQVvYbGnwm_w"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=92ed0fa59fc7a060';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, "\/authors\/shu.zhan?__cf_chl_rt_tk=_bke1x2zyA6BDz.5gijze.I4QMkF_03xBIYn7Of2Lkg-1744401531-1.0.1.1-nfzmHzajyAU12DBqd2equqlYP3PMtiXMJ9JtnhV9F4c" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>