Pafnuty Chebyshev

<h2 id="transcription">Transcription</h2>
The surname Chebyshev has been transliterated in several different ways, like Tchebichef, Tchebychev, Tchebycheff, Tschebyschev, Tschebyschef, Tschebyscheff, Čebyčev, Čebyšev, Chebysheff, Chebychov, Chebyshov (according to native Russian speakers, this one provides the closest pronunciation in English to the correct pronunciation in old Russian), and Chebychev, a mixture between English and French transliterations considered erroneous. It is one of the most well known data-retrieval nightmares in mathematical literature. Currently, the English transliteration Chebyshev has gained widespread acceptance, except by the French, who prefer Tchebychev. The correct <a href="/facts/Transliteration/1eemsW6o">transliteration</a> according to <a href="/facts/ISO_9/mDabFAYT">ISO 9</a> is Čebyšëv. The <a href="/facts/American_Mathematical_Society/fr5gotCt">American Mathematical Society</a> adopted the transcription Chebyshev in its <a href="/facts/Mathematical_Reviews/uP137L11">Mathematical Reviews</a>.<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a>
His first name comes from the <a href="/facts/Greek_language/pzDd6eIz">Greek</a> Paphnutius (Παφνούτιος), which in turn takes its origin in the <a href="/facts/Coptic_language/EzDloWDH">Coptic</a> Paphnuty (Ⲡⲁⲫⲛⲟⲩϯ), meaning "that who belongs to God" or simply "the man of God".

<h2 id="biography">Biography</h2>
<h3>Early years</h3>
One of nine children,<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a> Chebyshev was born in the village of Okatovo in the district of <a href="/facts/Borovsk/124Jyt3Y">Borovsk</a>, <a href="/facts/Province_of_Kaluga/S79jq6th">province of Kaluga</a>. His father, Lev Pavlovich, was a Russian nobleman and wealthy landowner. Pafnuty Lvovich was first educated at home by his mother Agrafena Ivanovna Pozniakova (in reading and writing) and by his cousin Avdotya Kvintillianovna Sukhareva (in <a href="/facts/French_language/qe1DnaQh">French</a> and <a href="/facts/Arithmetic/hvHwkbMV">arithmetic</a>). Chebyshev mentioned that his music teacher also played an important role in his education, for she "raised his mind to exactness and analysis".
<a href="/facts/Trendelenburg_gait/D2juP4Hc">Trendelenburg's gait</a> affected Chebyshev's adolescence and development. From childhood, he limped and walked with a stick and so his parents abandoned the idea of his becoming an officer in the family tradition. His disability prevented his playing many children's games and he devoted himself instead to mathematics.
In 1832, the family moved to <a href="/facts/Moscow/XUU6VkdY">Moscow</a>, mainly to attend to the education of their eldest sons (Pafnuty and Pavel, who would become lawyers). Education continued at home and his parents engaged teachers of excellent reputation, including (for mathematics and physics) the senior <a href="/facts/Moscow_University/xHPG4oau">Moscow University</a> teacher Platon Pogorelsky [ru], who had taught, among others, the future writer <a href="/facts/Ivan_Turgenev/9yWVfxoU">Ivan Turgenev</a>.

<h3>University studies</h3>
In summer 1837, Chebyshev passed the registration examinations and, in September of that year, began his mathematical studies at the second philosophical department of Moscow University. His teachers included <a href="/facts/Nikolai_Brashman/AQ8c6T1u">N.D. Brashman</a>, N.E. Zernov and D.M. Perevoshchikov of whom it seems clear that Brashman had the greatest influence on Chebyshev. Brashman instructed him in practical mechanics and probably showed him the work of French engineer <a href="/facts/Jean-Victor_Poncelet/zpd8aJJ8">J.V. Poncelet</a>.
In 1841 Chebyshev was awarded the silver medal for his work "calculation of the roots of equations" which he had finished in 1838. In this, Chebyshev derived an approximating algorithm for the solution of algebraic equations of nth degree based on <a href="/facts/Newton%2527s_method/VlRhI2FL">Newton's method</a>. In the same year, he finished his studies as "most outstanding candidate".
In 1841, Chebyshev's financial situation changed drastically. There was famine in Russia, and his parents were forced to leave Moscow. Although they could no longer support their son, he decided to continue his mathematical studies and prepared for the master examinations, which lasted six months. Chebyshev passed the final examination in October 1843 and, in 1846, defended his master thesis "An Essay on the Elementary Analysis of the Theory of Probability." His biographer Prudnikov suggests that Chebyshev was directed to this subject after learning of recently published books on probability theory or on the revenue of the Russian insurance industry.

<h3>Adult years</h3>
In 1847, Chebyshev promoted his thesis <a href="/facts/Pro_venia_legendi/VSEhfx78">pro venia legendi</a> "On integration with the help of logarithms" at <a href="/facts/St_Petersburg_University/s9purC6t">St Petersburg University</a> and thus obtained the right to teach there as a lecturer. At that time some of <a href="/facts/Leonhard_Euler/z2fsbjgj">Leonhard Euler</a>'s works were rediscovered by P. N. Fuss and were being edited by <a href="/facts/Viktor_Bunyakovsky/9KnrFINq">Viktor Bunyakovsky</a>, who encouraged Chebyshev to study them. This would come to influence Chebyshev's work. In 1848, he submitted his work The Theory of Congruences for a doctorate, which he defended in May 1849.<a class="footnote-ref" id="fnref:4" href="#fn:4">4</a> He was elected an <a href="/facts/Professor/JNqot4sU">extraordinary professor</a> at St Petersburg University in 1850, ordinary professor in 1860 and, after 25 years of lectureship, he became merited professor in 1872. In 1882 he left the university and devoted his life to research.
During his lectureship at the university (1852–1858), Chebyshev also taught practical mechanics at the <a href="/facts/Tsarskoye_Selo_Lyceum/Pv1qLV4c">Alexander Lyceum</a> in <a href="/facts/Tsarskoe_Selo/PqxvN72T">Tsarskoe Selo</a> (now Pushkin), a southern suburb of <a href="/facts/St_Petersburg/pNuCBxaM">St Petersburg</a>.
His scientific achievements were the reason for his election as junior <a href="/facts/Academician/E6Sywhsa">academician</a> (adjunkt) in 1856. Later, he became an extraordinary (1856) and in 1858 an ordinary member of the <a href="/facts/Russian_Academy_of_Sciences/RuUqhtFb">Imperial Academy of Sciences</a>. In the same year he became an honorary member of <a href="/facts/Moscow_University/xHPG4oau">Moscow University</a>. He accepted other honorary appointments and was decorated several times. In 1856, Chebyshev became a member of the scientific committee of the ministry of national education. In 1859, he became an ordinary member of the ordnance department of the academy with the adoption of the headship of the commission for mathematical questions according to ordnance and experiments related to ballistics. The <a href="/facts/French_Academy_of_Sciences/zF42DYQv">Paris academy</a> elected him corresponding member in 1860 and full foreign member in 1874. In 1878, Chebyshev presented a paper on garment cutting, inspired by a lecture by <a href="/facts/%25C3%2589douard_Lucas/NTC4y2N0">Édouard Lucas</a>, to the French Association for the Advancement of the Sciences.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a>
In 1893, he was elected honorable member of the <a href="/facts/St._Petersburg_Mathematical_Society/9141R4xv">St. Petersburg Mathematical Society</a>, which had been founded three years earlier.
Chebyshev died in <a href="/facts/St_Petersburg/pNuCBxaM">St Petersburg</a> on 8 December 1894.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a><a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>

<h2 id="mathematical-contributions">Mathematical contributions</h2>

Chebyshev is known for his work in the fields of <a href="/facts/Probability/fgYvMhwb">probability</a>, <a href="/facts/Statistics/DNPsKGYU">statistics</a>, <a href="/facts/Mechanics/A3yHLQA5">mechanics</a>, and <a href="/facts/Number_theory/zhoa7zrc">number theory</a>. The <a href="/facts/Chebyshev_inequality/jf5ReDJv">Chebyshev inequality</a> states that if 
 
 
 
 X
 
 
 {\displaystyle X}
 
 is a <a href="/facts/Random_variable/TwTBXnLT">random variable</a> with <a href="/facts/Standard_deviation/qSug9BRl">standard deviation</a> σ > 0, then the probability that the outcome of 
 
 
 
 X
 
 
 {\displaystyle X}
 
 is 
 
 
 
 d
 =
 k
 σ
 
 
 {\displaystyle d=k\sigma }
 
 or more away from its mean is at most 
 
 
 
 1
 
 /
 
 
 k
 
 2
 
 
 =
 
 σ
 
 2
 
 
 
 /
 
 
 d
 
 2
 
 
 
 
 {\displaystyle 1/k^{2}=\sigma ^{2}/d^{2}}
 
:

Pr
        (
        
          |
        
        X
        −
        
          
            E
          
        
        (
        X
        )
        
          |
        
        ≥
        d
         
        )
        ≤
        
          
            
              σ
              
                2
              
            
            
              d
              
                2
              
            
          
        
        .
      
    
    {\displaystyle \Pr(|X-{\mathbf {E} }(X)|\geq d\ )\leq {\frac {\sigma ^{2}}{d^{2}}}.}

The Chebyshev inequality is used to prove the <a href="/facts/Weak_law_of_large_numbers/X3Bjcy3v">weak law of large numbers</a>.
The <a href="/facts/Bertrand%2527s_postulate/8z3837xk">Bertrand–Chebyshev theorem</a> (1845, 1852) states that for any 
 
 
 
 n
 >
 3
 
 
 {\displaystyle n>3}
 
, there exists a <a href="/facts/Prime_numbers/L20FLkgn">prime number</a> 
 
 
 
 p
 
 
 {\displaystyle p}
 
 such that 
 
 
 
 n
 <
 p
 <
 2
 n
 
 
 {\displaystyle n<p<2n}
 
. This is a consequence of the Chebyshev inequalities for the number 
 
 
 
 π
 (
 n
 )
 
 
 {\displaystyle \pi (n)}
 
 of <a href="/facts/Prime_numbers/L20FLkgn">prime numbers</a> less than 
 
 
 
 n
 
 
 {\displaystyle n}
 
:

for 
 
 
 
 x
 
 
 {\displaystyle x}
 
 sufficiently large, 
 
 
 
 A
 
 
 x
 
 log
 ⁡
 (
 x
 )
 
 
 
 <
 π
 (
 x
 )
 <
 
 
 
 6
 A
 
 5
 
 
 
 
 x
 
 log
 ⁡
 (
 x
 )
 
 
 
 
 
 , with 
 
 
 A
 ≈
 0.92129.
 
 
 {\displaystyle A{\frac {x}{\log(x)}}<\pi (x)<{\frac {6A}{5}}{\frac {x}{\log(x)}}\;{\text{, with }}\;A\approx 0.92129.}
 
<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>
Fifty years later, in 1896, the celebrated <a href="/facts/Prime_number_theorem/3KA9egls">prime number theorem</a> was proved, independently, by <a href="/facts/Jacques_Hadamard/TgCkP3AE">Jacques Hadamard</a><a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and <a href="/facts/Charles_Jean_de_la_Vall%25C3%25A9e_Poussin/mvgoSbmM">Charles Jean de la Vallée Poussin</a>:<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>

lim
          
            x
            →
            ∞
          
        
        
          
            
              
              π
              (
              x
              )
              log
              ⁡
              (
              x
              )
              
            
            
              x
              
            
          
        
        =
        1
      
    
    {\displaystyle \lim _{x\to \infty }{\frac {\;\pi (x)\log(x)\;}{x\;}}=1}

using ideas introduced by <a href="/facts/Bernhard_Riemann/oV2fL0k8">Bernhard Riemann</a>.
Chebyshev is also known for the <a href="/facts/Chebyshev_polynomial/HoBINqgC">Chebyshev polynomials</a> and the <a href="/facts/Chebyshev_bias/sW8aw7zB">Chebyshev bias</a> – the difference between the number of primes that are congruent to 3 (modulo 4) and 1 (modulo 4).<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>
Chebyshev was the first person to think systematically in terms of <a href="/facts/Random_variables/TwTBXnLT">random variables</a> and their <a href="/facts/Moment_(mathematics)/GL7vJ1nb">moments</a> and <a href="/facts/Expected_value/1XV0JKL8">expectations</a>.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>

<h2 id="legacy">Legacy</h2>

Chebyshev is considered to be a founding father of <a href="/facts/Russia/jfkCwyxn">Russian</a> mathematics.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> Among his well-known students were the mathematicians <a href="/facts/Dmitry_Grave/APssNjqn">Dmitry Grave</a>, <a href="/facts/Aleksandr_Korkin/3oNhWrly">Aleksandr Korkin</a>, <a href="/facts/Aleksandr_Lyapunov/1b0TlYBz">Aleksandr Lyapunov</a>, and <a href="/facts/Andrey_Markov/F409PDqD">Andrei Markov</a>. According to the <a href="/facts/Mathematics_Genealogy_Project/J7AFo1Do">Mathematics Genealogy Project</a>, Chebyshev has 17,533 mathematical "descendants" as of January 2025.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>
The lunar crater <a href="/facts/Chebyshev_(crater)/pDvE8cxH">Chebyshev</a> and the asteroid <a href="/facts/2010_Chebyshev/DTaljxjH">2010 Chebyshev</a> were named to honor his major achievements in the mathematical realm.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>

<h2 id="publications">Publications</h2>
<ul><li>Tchebychef, P. L. (1899), Markov, Andrey Andreevich; Sonin, N. (eds.), <a href="https://archive.org/stream/oeuvresdepltche01chebrich">Oeuvres</a>, vol. I, New York: Commissionaires de l'Académie impériale des sciences, <a href="/facts/MR_(identifier)/uP137L11">MR</a> <a href="https://mathscinet.ams.org/mathscinet-getitem?mr=0147353">0147353</a>, Reprinted by Chelsea 1962</li>
<li>Tchebychef, P. L. (1907), Markov, Andrey Andreevich; Sonin, N. (eds.), <a href="https://books.google.com/books?id=1mBtAAAAMAAJ">Oeuvres</a>, vol. II, New York: Commissionaires de l'Académie impériale des sciences, <a href="/facts/MR_(identifier)/uP137L11">MR</a> <a href="https://mathscinet.ams.org/mathscinet-getitem?mr=0147353">0147353</a>, Reprinted by Chelsea 1962</li>
<li>Butzer, Paul; Jongmans, Francois (1999), "P. L. Chebyshev (1821–1894): A Guide to his Life and Work", Journal of Approximation Theory, 96: 111–138, <a href="/facts/Doi_(identifier)/muM9Etpq">doi</a>:<a href="https://doi.org/10.1006%2Fjath.1998.3289">10.1006/jath.1998.3289</a></li></ul>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_things_named_after_Pafnuty_Chebyshev/updAxRkj">List of things named after Pafnuty Chebyshev</a></li></ul>

<h2 id="further-reading">Further reading</h2>
<ul><li>Papadopoulos, Athanase (14 May 2019). <a href="https://bhavana.org.in/pafnuty-chebyshev-1821-1894/">"Pafnuty Chebyshev (1821-1894)"</a>. Bhāvanā – The mathematics magazine. The Bhavana Trust. Retrieved 25 November 2024.</li></ul>
<h2 id="external-links">External links</h2>
<ul><li> Media related to Pafnuty Chebyshev at Wikimedia Commons</li></ul>

<a href="/facts/Wikisource/TrMdylNf">Wikisource</a> has the text of the <a href="/facts/Encyclop%25C3%25A6dia_Britannica_Eleventh_Edition/mPElbCRY">1911 Encyclopædia Britannica</a> article "Chebichev, Pafnutiy Lvovich".

<ul><li><a href="https://tcheb.ru">Mechanisms by Chebyshev</a> – short 3d films – embodiment of Tchebishev's inventions</li>
<li><a href="https://mathgenealogy.org/id.php?id=12542">Pafnuty Chebyshev</a> at the <a href="/facts/Mathematics_Genealogy_Project/J7AFo1Do">Mathematics Genealogy Project</a></li>
<li>O'Connor, John J.; <a href="/facts/Edmund_F._Robertson/jQMcnY79">Robertson, Edmund F.</a>, <a href="https://mathshistory.st-andrews.ac.uk/Biographies/Chebyshev.html">"Pafnuty Chebyshev"</a>, <a href="/facts/MacTutor_History_of_Mathematics_Archive/xtwLmN5q">MacTutor History of Mathematics Archive</a>, <a href="/facts/University_of_St_Andrews/IwXjmljw">University of St Andrews</a></li>
<li><a href="https://web.archive.org/web/20060829211200/http://www.bashedu.ru/konkurs/tarhov/russian/chebish.htm">Biography</a>, <a href="http://www.mathsoc.spb.ru/pantheon/chebyshe/b-e.html">another one</a>, and <a href="https://web.archive.org/web/20060713072728/http://www.univer.omsk.su/omsk/Edu/Math/chchebishev.htm">yet another</a> (all in <a href="/facts/Russian_language/ETXrTgHV">Russian</a>).</li>
<li><a href="https://archive.org/details/pltchbychefets00vasiuoft">Biography</a> in French.</li>
<li>Œuvres de P.L. Tchebychef <a href="https://archive.org/details/oeuvresdepltche01chebrich/">Vol. I</a>, <a href="https://archive.org/details/oeuvresdepltche02chebrich">Vol. II</a> (in <a href="/facts/French_language/qe1DnaQh">French</a>)</li>
<li><a href="https://www.youtube.com/watch?v=1EoUBwwl8-k">When Mathematicians use Geometry to Cut Cloth</a> – A presentation by <a href="/facts/%25C3%2589tienne_Ghys/UX88qUQo">Étienne Ghys</a> on the work of Chebyshev, with a special focus on his research on Chebyshev nets in <a href="/facts/Differential_geometry/c04XmyLu">differential geometry</a>.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Pafnuty Lvovich Chebyshev – Britannica Online Encyclopedia <a href="http://www.britannica.com/eb/article-9022729/Pafnuty-Lvovich-Chebyshev" target="_blank">http://www.britannica.com/eb/article-9022729/Pafnuty-Lvovich-Chebyshev</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Chebyshev, Pafnutiĭ L'vovich, on MathSciNet. <a href="https://mathscinet.ams.org/mathscinet/search/author.html?mrauthid=191693" target="_blank">https://mathscinet.ams.org/mathscinet/search/author.html?mrauthid=191693</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Biography in MacTutor Archive <a href="http://www-history.mcs.st-andrews.ac.uk/Biographies/Chebyshev.html" target="_blank">http://www-history.mcs.st-andrews.ac.uk/Biographies/Chebyshev.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Pafnuty Chebyshev. Encyclopaedia Britannica <a href="https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev" target="_blank">https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">Tapia, Victor (2025). "Chebyshev and Garment Cutting: Debunking Some Myths". The Mathematical Intelligencer: 1–5. doi:10.1007/s00283-025-10409-x. <a href="https://link.springer.com/article/10.1007/s00283-025-10409-x" target="_blank">https://link.springer.com/article/10.1007/s00283-025-10409-x</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Pafnuty Chebyshev. Encyclopaedia Britannica <a href="https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev" target="_blank">https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">"Pafnuty Lvovich Chebyshev". MacTutor. Retrieved 22 November 2024. <a href="https://mathshistory.st-andrews.ac.uk/Biographies/Chebyshev/" target="_blank">https://mathshistory.st-andrews.ac.uk/Biographies/Chebyshev/</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Tchebichef (1852). "Mémoire sur les nombres premiers". Journal de Mathématiques Pures et Appliquées (in French): 366–390. ISSN 1776-3371. Retrieved 26 November 2024. English translation by Mike Bertrand (November 5, 2020). <a href="https://eudml.org/doc/234762" target="_blank">https://eudml.org/doc/234762</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Hadamard, Jacques (1896), "Sur la distribution des zéros de la fonction ζ(s) et ses conséquences arithmétiques.", Bulletin de la Société Mathématique de France, 24, Société Mathématique de France: 199–220, archived from the original on 10 September 2024 <a href="/wiki/Jacques_Hadamard" target="_blank">/wiki/Jacques_Hadamard</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">de la Vallée Poussin, Charles-Jean (1896), "Recherches analytiques sur la théorie des nombres premiers.", Annales de la Société scientifique de Bruxelles, 20 B, 21 B, Imprimeur de l'Académie Royale de Belgique: 183–256, 281–352, 363–397, 351–368 <a href="/wiki/Charles_Jean_de_la_Vall%C3%A9e_Poussin" target="_blank">/wiki/Charles_Jean_de_la_Vall%C3%A9e_Poussin</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Rubinstein, Michael; Sarnak, Peter (1994). "Chebyshev's Bias". Experimental Mathematics. 3 (3): 173–197. doi:10.1080/10586458.1994.10504289. ISSN 1058-6458. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Mackey, George (July 1980). "Harmonic analysis as the exploitation of symmetry-a historical survey". Bulletin of the American Mathematical Society. New Series. 3 (1): 549. doi:10.1090/S0273-0979-1980-14783-7. hdl:1911/63317. <a href="https://doi.org/10.1090%2FS0273-0979-1980-14783-7" target="_blank">https://doi.org/10.1090%2FS0273-0979-1980-14783-7</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Pafnuty Chebyshev. Encyclopaedia Britannica <a href="https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev" target="_blank">https://www.britannica.com/biography/Pafnuty-Lvovich-Chebyshev</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Pafnuty Chebyshev at the Mathematics Genealogy Project <a href="https://mathgenealogy.org/id.php?id=12542" target="_blank">https://mathgenealogy.org/id.php?id=12542</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">Schmadel, Lutz D. (2007). "(2010) Chebyshev". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 163. doi:10.1007/978-3-540-29925-7_2011. ISBN 978-3-540-00238-3. <a href="978-3-540-00238-3" target="_blank">978-3-540-00238-3</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
</ol>

Pafnuty Chebyshev open-in-new

Pafnuty Chebyshev