[Bug-apl] Alpha-underbar doesn't work in lambda functions

[Elias Mårtenson]

I'm doing a simple test with alpha-underbar in a lambda function and
getting an error message. To reproduce:

      *F ← { ⍺ ⍶ ⍵ }*
      *10 + F 20*
VALUE ERROR
F[1]  λ←⍺ ⍶ ⍵
          ^

Regards,
Elias