The Picard number of a Kummer K3 surface
Let be a separably closed field of characteristic not
, and
an abelian surface. Then it is a basic fact (e.g. see Example 1.3 (iii) of Huybrechts’ “K3 Surfaces”) that one can make a K3 surface out of
. The construction is as follows. Consider the involution
given by
The …