In the sequent systems for exponential-free linear logic and BCK logic a procedure of elimination of maximum cuts, cuts which correspond to maximum segments from natural deduction derivations, will be presented.

The well-known picture that sequent derivations without cuts and normal derivations “are the same” will be changed. Sequent derivations without maximum cuts (i.e. special cuts which correspond to maximum segments from natural deduction) will be considered. It will be shown that the natural deduction image of a sequent derivation without maximum cuts is a normal derivation, and the sequent image of a normal derivation is a derivation without maximum cuts. The main consequence of that property will be that sequent derivations (...) without maximum cuts and normal derivations “are the same”. (shrink)

A special kind of maximum cuts in sequent derivations, actual maximum cuts, is defined. It is shown that (1) each actual maximum cut of a sequent derivation makes maximum segments in its natural deduction image, and (2) each maximum segment of a natural deduction derivation makes an actual maximum cut in its sequent image.