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Indexing Structural/Selection
x[y]  x⌷y   x↑y  x↓y  ⌽y  x⌽y  b⌿y …
general
random access
slower
specific
restricted access
faster

   x←?1e5⍴2e9
   i←(¯1+⍴x)-⍳⍴x
   x[i]≡⌽x
1
   cmpx 'x[i]' '⌽x'
  x[i] → 5.45E¯4 |   0% ⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕⎕
  ⌽x   → 2.29E¯4 | -59% ⎕⎕⎕⎕⎕⎕⎕⎕