A c.U*-geometry is a geometry over the diagram c.L*, the point residues of which are finite dual unitals. Only one flag-transitive example is known. Its full automorphism group is Aut(J(2)), but J(2) also acts flag-transitively on it. We shall prove that this geometry is indeed the unique flag-transitive c.U*-geometry, thus obtaining a new geometric characterization of the Hall-Janko group J(2).
Huybrechts, C., Pasini, A. (1998). A characterization of the Hall-Janko group J2 by a c.L*-geometry. In Groups and Geometries (pp. 91-106). BASEL : Birkhauser.
A characterization of the Hall-Janko group J2 by a c.L*-geometry
PASINI A.
1998-01-01
Abstract
A c.U*-geometry is a geometry over the diagram c.L*, the point residues of which are finite dual unitals. Only one flag-transitive example is known. Its full automorphism group is Aut(J(2)), but J(2) also acts flag-transitively on it. We shall prove that this geometry is indeed the unique flag-transitive c.U*-geometry, thus obtaining a new geometric characterization of the Hall-Janko group J(2).
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https://hdl.handle.net/11365/13440
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