The most recent version of this documentation can be found at https://docs.dyalog.com/20.0/.

Left Tack
Monadic Left Tack means

Same

      ⊣  1 2 3
1 2 3
Dyadic Left Tack means

Left

      'L' ⊣ 'R'
L
      ⊣/ 1 2 3
1

Language Elements