A supersingular K3 surface in characteristic 2 and the Leech
lattice -- Shigeyuki Kondo, March 4, 2011 

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We construct a K3 surface over an algebraically closed field of
characteristic 2 which contains two sets of 21 disjoint smooth
rational curves such that each curve from one set intersects
exactly 5 curves from the other set.  We also give a
description of the group of automorphisms of the K3 surface,
and a relation with an even definite unimodular lattice of rank
24 called the Leech lattice.  This is joint work with
I. Dolgachev and T. Katsura.