I like the second of the proposed solutions. Since ambivalent function can always be called monadically, I think that making the header of d-fns always λ←⍺ λ1 ⍵ regardless of whether ⍺ occurs in the body or not, shouldn't break anything and would only make a language a bit simpler. Although maybe a bit less consistent, because there would still be a need to distinguish d-ops.
-k
