On Natural Deduction v. Sequenzen, Mitchell Wand's comment.
>From Roger Hindley
I would call a system in which the assumptions Gamma appeared
as a set, rather than a sequence, "excellent"!
But it is a mathematician's formulation; if the system was
implemented mechanically, sequence-handling rules would
have to be added.
Also, there has been always some interest in ssystems in which
the structural rules are present only in a weak form (perhaps
no duplication of premises allowed, or no weakening, etc.)
So it seems best to always make explicitly clear that one's
system is not restricted, if it isn't.
(Of course these comments are not intended for the expert,
to whom all the distinctions involved will be clear anyway.
But there might be some beginner reading this rubbish,
to whom they aren't.