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At is a Dyadic operator

Operator At means

At

      (0@2 4) 1 2 3 4 5
1 0 3 0 5

      10 (×@2 4) 1 2 3 4 5
1 20 3 40 5

      (÷@2 4) 1 2 3 4 5
1 0.5 3 0.25 5

      '*'@(2∘|) 1 2 3 4 5   ⍝ Boolean selection 1 0 1 0 1
* 2 * 4 *

      ⌽@(2∘|) 1 2 3 4 5     ⍝ Reversal of sub-array 1 3 5
5 2 3 4 1