Orbits in the anti-invariant sublattice of the K3-lattice
-- Ali Sinan Sertöz

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We determine the number of
orbits of primitive vectors in the anti-invariant sublattice of the K3-lattice
under the action of isometries. In particular when this K3 surface covers an
Enriques surface we draw geometric conclusions about the orbits of curves which
do not descend down to the Enriques surface.