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: '92df6edc1f836ba2',cH: 'pkn3PPMGfh3Ljaq.XyyIPqFZ0MzRXCNvI5q0GJv5ldc-1744258631-1.2.1.1-gfI1uY4O_VpYKzZzMzwi7ATppCkpjlZmannzVW5fjqO7jOpJN_N4FAsWpQoQbnR3',cUPMDTk: "\/authors\/xu.jun.2?__cf_chl_tk=N.SXZGUl4IpiVKU9eKc_Yd_whQbNOzMI5CbMFnDb6Ys-1744258631-1.0.1.1-WlFjT3aa7VV2zdkf5qUQ9Ap924zwF7V_EoZ4Q3CIqu0",cFPWv: 'b',cITimeS: '1744258631',cTTimeMs: '1000',cMTimeMs: '390000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "unsupported_browser_beacon",fa: "\/authors\/xu.jun.2?__cf_chl_f_tk=N.SXZGUl4IpiVKU9eKc_Yd_whQbNOzMI5CbMFnDb6Ys-1744258631-1.0.1.1-WlFjT3aa7VV2zdkf5qUQ9Ap924zwF7V_EoZ4Q3CIqu0",md: "3H2L4fqybiy3SHyvrY1dUaQSKZup3KMqKIXu__vJ94o-1744258631-1.2.1.1-Gd9aEsS5wuGQsTBvngY1JAkSuZVwFPD7jqZ3Up8IdC9fAknDNYJHvQ0mSEKm0wHokccmuUutSZj2PT8esXL0R0l1jvbOUtTAqX0Tqb.sc153IFsxG0azn54cjjwTIQxO_eJ0wUj5rtfg.HnhCZ8.Ipb0S9fCIGkRwegZgM53GYZcE9CrMq40abdxWSypDXKIn.bFCSNoQI42B7W2P03l8DWl7OPK3qVU6HIjbOh5.X_lSYk0eXlFVVpNneCXK02QLDkchVNtrIO0o1NFDv4maaovjKBTw_kyxw2GbaRjha9hEbNBf_4vBEtboZhR4M_dqpE2._T2jOMpkqli.fI_BafdjOhaPT34OcMZ0c5uk7lSx8mKzZAWHzZHU7O0Jlug9Cy0wtXSulaAMY1P8Z6mSb68BPVHVll0XbODxhtPmaHaVHoBLw6ODvlJhNXQycFKCHRdxypF7vTBCE8wOkFvsFTVvf22BdtNUCqIRQ7sUXTjzlooCWtym7s9I77N_B46VIAdCNdSqRCNHZB0tPAalgTZ64cRCo3AaykPkov0UHxgrr077bF3hVAcqq_KgtgkjAIIhIQWRx9NyJrPG5X2KUKjzU_M_tKhjaj1XWOaeEsHqbbDwliQUBoBFpxpjP0hiFCkX39GzDCvNOatbsPFwr4hrmu8ikLQbcvVVB1Ub20NxsCt3LDpODQtVWxmnLzqErGjVzglH4b_Ddjs5uVE5so1AaUD9Peqv3lwf_dvNdGLBpJ7kChXD6ofx2vUEkoVMPcuNU1dUQvDcWHXROBCjPTkyOq4RkCIBjgZBpBJ4L7tiYJ6LAZxPNfp89zGWUG6PBkxS8PCnbJJwxalrsh0sIkndSYeq6KC5JKRpCYdCasp_pM.eAKakrMVIRxJB7RYPS.YSsiDWdA4Rl04F0HsZAKI.xl__v7s5nllkcqYPRTauTRw3cB4DxG8PgBSwBqg1KZ8JdKBhRjmrm5Zz6XYQ3ZcGMCXKx0geFoOwkQHDa_Xm_9pHBQ8JEJjibBOx9WhKMTPQix2u23DfwTlLfNmMJ6zVEJKquJlGdgnlamqEMv5zpOY0ofYrThvIq2Q8udu81P4mI7de_Rg6n_6oB6rJwG1FTiQGKUqDnjqbD_HqY.12X1heGycUK2ox1SVfS4zLIg5XM_YvGtmCnkkLgFDhedMsvrBGAYYuDKVDO44B6Br2YrRNFKNxAxQvrcTs5GSYZOJb9hCkOxUDvq2gIgBgA",mdrd: "uyDBL6unGjbuTcUvIFMXWI2y4FG8TLSjfqqqtxd8Gf8-1744258631-1.2.1.1-Z5BFBm5d2UoCNZy3q_vIL1kgdd2MXzkqqXCF6JbvsJMU0yX_1PgTHBda3uwu0svGw2vr5AxIzmB04cjH_oZHcOWFJZc7Cg3cmtxihq0H4KZwD3b9WZtcf_BEJGlOtPKeGezjGQrbXHUTfJp5xqHOFRyAPUVGJGJkGkK9w3IPMxwYwxwiw3xdJzypBZM7wAVGWN.BW7pfpOUKGBpcrc3DN5xVSbMX7aBRodUnbmrKmBoIzpSONUL1giEVlG.YRwo0MQfMjDJg4E9wv.wMBnKqn_JPPSybrPyLAnsFU_BilZdSMjkw3eEWktOlroECPhO2_cZLaU21atImtGmJSb2PwBwwgAlx2oqBcWlaLTmf24zRBWp6APSySmI53KU9TsmRoy.UtmShfYjdv2p9wMa2OaoGTdM0leHkokmUX.0NM4YOWFLL91W.Ly2cGyA3Xc_PGTsIAI7F12sh3LJ6kyXnxmVC5qYXQujqvm3rC.oFcvina08y7TaEchGBolwR.v7IQXhzIVMsQwHZz1dyGNIOekfcnrmgConPbiYAAFMW4cKVEtEUpxB3ioQFSMpVikwwoDaIRDPadYWjsfLH0gE5Cf3IPT72CCXP99sImpfiE76dckHO4eWds_tHhNB9cJK.if5tq_uUB7c4.F.zR094BWeKmZC4A_p9BrBOU4M0DnXahraZzI85_DVPx_uKlT8oeCdllaxfA17eCCfEfDpSDCA2bugS4Ptdq32ktIrPtB5vMozmUF0T0JpkO0AgsQtkKDNP2vtHnRxb37vxQm86nv94cdnClMvE2Dt7sZ7m23heOl3Uy9.Cur6ekXXsBLKOBWKRIza2suvOX_u3bk4Yoio5HRvijVfjl7cr3K4bk_i3w_X6Ipsj0fLd7reIcdnU9986zldMarGbKMeOqDdqDYy4xHRt8ajjIo817HSwm1aljU2HpFmzZYE5ADLpAyN_Fq0Ayw5iLsdUCA4PC__53l22HF9Rp8Cr.oHRHV2CWeGQXtQ6pYWx_xEkewf1TFWF2SBKcSQHbheGS1pUl6wmyh4iAVzJ8MAJ3EnHrf7Kt8fFxQOXpooFaaMGvzP5y7EM_cUBgb3m3J0vCvTVcI7w5HLtP1U16nO4gRLjYczfbYOzmM7EEHwRpWFO3TkH6rvOOqEuZNhFYWipzI2RR1foc7acZVwqf2ZfeP3FRccgwrJQqkkRiefSO2d5Ld9L2HtWtvVPLj3NnXYvwjvms9EVOtjVkYyKs.XQZPptv6yKe0wizVVhX6mKoHeQ7zWy.sR6YcXXzzXQnV6jPUHJW3bgOc6.EtgepvBrKLvRoDtrRYrHkvaMSFBmKTHqOUOGZqiDa9MwLHf.lzLgv3Z1unQpQrqzFrVAiIwgumIsy0l4d_rJcvOmmc9zMnKuTjvcyQnN8JlhxonsK7xlOi_jKHtGHRKYI8vOZ8jeSQ_Ukvrca3ViMHHORmBATJE7oWULzz0Jgu6JWIdXqSjik2_vxyDHr710DJZAsNHvl_RNGzHa2nBnbGHNIKXWrU89o4Juaz2MQd7p4vIfP6leOSF3grGFV.kFw7WQlvPlQ1FGxmq0b8rJDUj0yNRBlZ23ZddpBm50BqrunGfmHv0bU2vCqiLhUVrrvRJCzdpDndDbfbJAKkv5Ad8v9PTset9KfSkhDqbjDjFhKWsirVx3qZgNwcb8_SJZSbWSMXJKxyivwxewFqc.ZjpMFFQ952QaZSDlPIUPoqmVMd.iMMSwlEQQUF0n1IU7x9upA0NqIaNKJqMxFh_coTPmYWVPA3sO11xIX33TjF0waXkbjWNbB4m0N0jOcZ7hgdaRtjL3Di5.gzfo8bii2J0y_q_2XCjH6u3U9_UaO3pqiluCzivb8cYpcZsJRcsOrXC9WY.9lh_hQTyYm1bqyZK46.fxPP01THS9v43n.k7A.eWUb0fnpIPPHfGVRJzoSvXTzth__nuwLMVylVsBdyJBnkF2AB2dO_TDfLjwB2huniiQis30OWAP_Ob6.um0T7lbZtcQ5YZaxRYB2dJsZns1StzdAs0e5JD1wFWx"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=92df6edc1f836ba2';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\/xu.jun.2?__cf_chl_rt_tk=N.SXZGUl4IpiVKU9eKc_Yd_whQbNOzMI5CbMFnDb6Ys-1744258631-1.0.1.1-WlFjT3aa7VV2zdkf5qUQ9Ap924zwF7V_EoZ4Q3CIqu0" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>