⍺⍺
In a defined operator, ⍺⍺ denotes its left operand: function or array.
apply←{⍺⍺ ⍵} ⋄ (-apply)3 ⍝ ¯3 add←{⍺⍺+⍵} ⋄ (10 add)3 ⍝ 13
⍺ and ⍵ remain the derived function’s arguments.
⍺
⍵