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Constant R←{X}(A⍨)Y

A,  X and Y are arrays. The Constant operator returns array A.

Examples:

      'mu'⍨ 'any' ⎕NULL   ⍝ Always returns its operand
mu
      1E100 ('mu'⍨) 1j1
mu
      ¯1⍨¨ ⍳2 3
¯1 ¯1 ¯1
¯1 ¯1 ¯1