Talked to Dan Licata a bit today about natural deduction. I continually find out I don't ever really understand the very foundations of my field as much as I think I do. The ambifortunate thing is, according to Bob's offhand comment, that the scarcely articulatable mystery confounding me about why normal natural deductions conflate certain cut-free sequent proofs is what got Girard to invent proof nets. So maybe the answer's hiding there, but arghhhhh classical nonjudgmental presentations of linear logic.