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</math>
where the infimum is taken over all rational functions of degree <math>(K, K)</math>.<ref name=":5" /> This approximation problem is related to several results in [[potential theory]],<ref>{{Cite book|title=Logarithmic potentials with external fields|last1=Saff|first1=E.B.|last2=Totik|first2=V.|publisher= Springer Science & Business Media |isbn=9783662033296|___location=Berlin|oclc=883382758|date = 2013-11-11}}</ref><ref>{{Cite journal|last=Gonchar|first=A.A.|date=1969|title=Zolotarev problems connected with rational functions|journal= Mathematics of the USSR-Sbornik|volume=7|issue=4|pages=623–635|bibcode=1969SbMat...7..623G|doi=10.1070/SM1969v007n04ABEH001107}}</ref> and was solved by [[Yegor Ivanovich Zolotarev|Zolotarev]] in 1877 for <math>E</math> = [a, b] and <math> F=-E.</math><ref>{{Cite journal|last=Zolotarev|first=D.I.|date=1877|title=Application of elliptic functions to questions of functions deviating least and most from zero|journal=Zap. Imp. Akad. Nauk. St. Petersburg|volume=30|pages=1–59}}</ref> The solution is also known when <math> E</math> and <math> F</math> are disjoint disks in the complex plane.<ref>{{Cite journal|last=Starke|first=Gerhard|date=July 1992|title=Near-circularity for the rational Zolotarev problem in the complex plane|journal=Journal of Approximation Theory|volume=70|issue=1|pages=115–130|doi=10.1016/0021-9045(92)90059-w|issn=0021-9045|doi-access=free}}</ref>
==== Heuristic shift-parameter strategies ====
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