NB: More recent documentation for Dyalog APL is available at https://docs.dyalog.com/20.0/.

Right Tack ⊢
Monadic Right Tack means

Same 

      ⊢  1 2 3
1 2 3
Dyadic Right Tack means

Right 

      'L' ⊢ 'R'
R
      ⊢/ 1 2 3
3

Language Elements