Editing Palindrome (section)

{{Short description|Sequence that reads the same forwards and backwards}}
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[[File:Ambigram_palindrome_ΝΙΨΟΝΑΝΟΜΗΜΑΤΑΜΗΜΟΝΑΝΟΨΙΝ_(Wash_your_sins,_not_only_your_face,_in_Greek).jpg|thumb|upright=1.3|The 4th-century Greek Byzantine palindrome: [[ΝΙΨΟΝ ΑΝΟΜΗΜΑΤΑ ΜΗ ΜΟΝΑΝ ΟΨΙΝ]] (''Wash Your Sins, Not Only Your Face'') on a mosaic in the {{ill|Monastery of Malevi|el|Μονή Μαλεβής Αρκαδίας}} in Greece.]]
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A '''palindrome''' ([[Help:IPA/English|/ˈpæl.ɪn.droʊm/]]) is a word, [[palindromic number|number]], phrase, or other sequence of symbols that reads the same backwards as forwards, such as ''[[madam]]'' or ''[[racecar]]'', the date "[[Twosday|02/02/2020]]" and the sentence: "A man, a plan, a canal – [[Panama]]".  The 19-letter [[Finnish language|Finnish]] word ''saippuakivikauppias'' (a [[soapstone]] vendor) is the longest single-word palindrome in everyday use, while the 12-letter term ''tattarrattat'' (from [[James Joyce]] in ''[[Ulysses (novel)|Ulysses]]'') is the longest in English.

The word ''palindrome'' was introduced by English poet and writer [[Henry Peacham (born 1578)|Henry Peacham]] in 1638.<ref name="p. 123">Henry Peacham, ''The Truth of our Times Revealed out of One Mans Experience'', 1638, [https://quod.lib.umich.edu/cgi/t/text/pageviewer-idx?cc=eebo;c=eebo;idno=a09207.0001.001;node=A09207.0001.001:5;seq=134;submit=Go;type=simple;vid=14563;q1=palindrome;page=root;view=text p. 123] {{Webarchive|url=https://web.archive.org/web/20200714022850/https://quod.lib.umich.edu/cgi/t/text/pageviewer-idx?cc=eebo;c=eebo;idno=a09207.0001.001;node=A09207.0001.001:5;seq=134;submit=Go;type=simple;vid=14563;q1=palindrome;page=root;view=text |date=14 July 2020 }} </ref>  The concept of a palindrome can be dated to the 3rd-century BCE, although no examples survive. The earliest known examples are the 1st-century CE Latin [[acrostic]] [[word square]], the [[Sator Square]] (which contains both word and sentence palindromes), and the 4th-century Greek Byzantine sentence palindrome ''[[nipson anomemata me monan opsin]].''<ref name="Triantaphylides Dictionary">{{Cite web|url=http://www.greek-language.gr/greekLang/modern_greek/tools/lexica/search.html?lq=%CE%BA%CE%B1%CF%81%CE%BA%CE%B9%CE%BD%CE%B9%CE%BA%CF%8C%CF%82&dq=|title=Combined word search for καρκινικός|last=Triantaphylides Dictionary|first=Portal for the Greek Language|website=www.greek-language.gr|access-date=6 May 2019|archive-date=6 May 2019|archive-url=https://web.archive.org/web/20190506110047/http://www.greek-language.gr/greekLang/modern_greek/tools/lexica/search.html?lq=%CE%BA%CE%B1%CF%81%CE%BA%CE%B9%CE%BD%CE%B9%CE%BA%CF%8C%CF%82&dq=|url-status=live}}</ref><ref name="Greece 1814, p. 85">[[William Martin Leake]], ''Researches in Greece'', 1814, p. 85</ref>

Palindromes are also found in music (the [[table canon]] and [[crab canon]]) and biological structures (most [[genomes]] include [[Palindromic sequence|palindromic gene sequences]]). In [[automata theory]], the set of all palindromes over an [[alphabet]] is a [[context-free language|context-free]] language, but it is not [[Regular language|regular]].