Iota
Monadic Iota means

Index Generator

      ⍳ 10
1 2 3 4 5 6 7 8 9 10

      ⍳ 2 3
┌───┬───┬───┐
│1 1│1 2│1 3│
├───┼───┼───┤
│2 1│2 2│2 3│
└───┴───┴───┘
Dyadic Iota means

Index Of

      'ABCDABCDEF' ⍳ 'ACF'
1 3 10

      mat
1 2
3 4
5 6
      mat ⍳ 5 6
3

Language Elements