ar X iv : a lg - g eo m / 9 41 20 13 v 1 1 4 D ec 1 99 4 EVEN LINKAGE CLASSES

In this paper the author generalizes the E and N -type resolutions used by Martin-Deschamps and Perrin [10] to subschemes of pure codimension in projective space, and shows that these resolutions are interchanged by the mapping cone procedure under a simple linkage. Via these resolutions, Rao’s correspondence is extended to give a bijection between even linkage classes of subschemes of pure codimension two and stable equivalence classes of reflexive sheaves E satisfying H ∗ (E) = 0 and Ext(E,O) = 0. Further, these resolutions are used to extend the work of Martin-Deschamps and Perrin for Cohen-Macaulay curves in P to subschemes of pure codimension two in Pn. In particular, even linkage classes of such subschemes satisfy the Lazarsfeld-Rao property and any minimal subscheme for an even linkage class links directly to a minimal subscheme for the dual class.