Japt, 11 9 bytes

à2 c
íUéJ

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Japt, 11 9 bytes

à2 c
íUéJ

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à2 c\níUéJ     :Implicit input of array U
à2             :Combinations of length 2
   c           :Flatten
    \n         :Reassign to U
      í        :Interleave with
       Ué      :  U rotated right
         J     :    -1 times (i.e., rotated left)

Japt, 11 bytes

iUà2)c ã2 â

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Japt, 11 9 bytes

à2 c
íUéJ

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Japt, 9 bytes

á2 c ã2 â

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Japt, 11 bytes

iUà2)c ã2 â

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