## Resolutions of convex geometries.(English)Zbl 1477.52001

Summary: Convex geometries [P. H. Edelman and R. E. Jamison, Geom. Dedicata 19, 247–270 (1985; Zbl 0577.52001)] are finite combinatorial structures dual to union-closed antimatroids or learning spaces. We define an operation of resolution for convex geometries, which replaces each element of a base convex geometry by a fiber convex geometry. Contrary to what happens for similar constructions – compounds of hypergraphs, as in [M. Chein et al., Discrete Math. 37, 35–50 (1981; Zbl 0478.05071)], and compositions of set systems, as in [R. H. Möhring and F. J. Radermacher, Ann. Discrete Math. None, 257–356 (1984; Zbl 0567.90073)] –, resolutions of convex geometries always yield a convex geometry.
We investigate resolutions of special convex geometries: ordinal and affine. A resolution of ordinal convex geometries is again ordinal, but a resolution of affine convex geometries may fail to be affine. A notion of primitivity, which generalize the corresponding notion for posets, arises from resolutions: a convex geometry is primitive if it is not a resolution of smaller ones. We obtain a characterization of affine convex geometries that are primitive, and compute the number of primitive convex geometries on at most four elements. Several open problems are listed.

### MSC:

 52A01 Axiomatic and generalized convexity 05B25 Combinatorial aspects of finite geometries 06A07 Combinatorics of partially ordered sets 51D20 Combinatorial geometries and geometric closure systems

### Citations:

Zbl 0577.52001; Zbl 0478.05071; Zbl 0567.90073
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