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(0{::(-:|.)\.#&amp;,&lt;\)~i.@#


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Explanation

(0{::(-:|.)\.#&amp;,&lt;\)~i.@#  Input: array of chars S
                       #  Length of S
                    i.@   Range, [0, 1, ..., len(S)-1]
(                 )~      Dyadic verb on range and S
           \.               For each outfix of S of size x in range
        |.                    Reverse
      -:                      Matches input (is palindrome)
                &lt;\          Box each infix of S of size x in range
             #&amp;,            Flatten each and copy the ones that match
 0{::                       Fetch the result and index 0 and return