Abstract. We characterize the curves in P 3 that are minimal in their biliaison class. Such curves are exactly the curves that do not admit an elementary descending biliaison. As a consequence we have that every curve in P 3 can be obtained from a minimal one by means of a finite sequence of ascending elementary biliaisons.
IntroductionLet C be a curve (i.e., a locally Cohen-Macaulay subscheme equidimensional of dimension 1) in P = P 3 k over an algebraically closed field k. Let J C be its ideal sheaf in O P andIn [9] P. Rao introduced the notion of a biliaison (even linkage) class of curves and proved that two curves C and C are in the same class if and only if HBefore stating the main results of the paper we recall some basic notions concerning biliaison. A good reference for the subject is [6] or [8]. Recall that two curves C and C are in the same biliaison class if there is an even number of linkages connecting them. Definition 1. A non-ACM curve C is said to be minimal (in its biliaison class) if, for every C in the same biliaison class, HDefinition 2. Let C be a curve and let Q be a surface containing it. A curve C is said to be obtained from C by an elementary biliaison on Q of height m if there are surfaces T and V of degrees t, t + m, respectively, such that C is linked to a curve D by means of (Q, T ) and D is linked to C by means of (Q, V ).