⍶
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.
⍺
⍵