⍺
⍺ is the current dfn’s left argument.
10{⍺-⍵}3 ⍝ 7
⍺←expression supplies a lazy default, evaluated only on monadic calls.
⍺←expression
{⍺←2 ⋄ ⍺×⍵}3 ⍝ 6 4{⍺←2 ⋄ ⍺×⍵}3 ⍝ 12