Monadic Up Arrow means

If ⎕ML<2 Mix

      ↑ 'Hip' 'Hop'
Hip
Hop
      ↑ (6 4) 5 3
6 4
5 0
3 0
      ↑[0.5] 'Hip' 'Hop'
HH
io
pp

If ⎕ML≥2 First

      ↑ (6 4) 5 3
6 4

Dyadic Up Arrow means

Take

      4 ↑ 'Pineapple'
Pine
      ¯5 ↑ 'Pineapple'
apple

      mat
1  2  3  4
5  6  7  8
9 10 11 12
      
      2 ¯3 ↑ mat
2 3 4
6 7 8

      ¯2 ↑ mat
5  6  7  8
9 10 11 12

      ¯2 3 ↑ 7
0 0 0
7 0 0

Language Elements