We construct a rank-$2$ indecomposable vector bundle on $\mathbb
P^2\times\mathbb P^2$ in characteristic $2$ that
does not come from a bundle on $\mathbb P^2$ by factor projection nor from a
bundle on $\mathbb P^{m} $
by central projection. We show that the zero-sets of a suitable twist of $E$
form
a family of nonclassical smooth Enriques surfaces of bidegree (4, 4) whose
general member is
‘singular’ in the sense that Frobenius acts isomorphically on $H^1$, and
there is a smooth divisor consisting of smooth supersingular surfaces
(Frobenius acts as zero). Every nonclassical Enriques surface of bidegree (4,
4) in $\mathbb P^2\times\mathbb P^2$ that is bilinearly normal arises as a
zero-set in this way.

Este artículo explora los viajes en el tiempo y sus implicaciones.

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