PhD ThesesIn this thesis we generalise the theory of exceptional covers of varieties to the context of
difference algebraic geometry. We formulate the notion of difference exceptional covers
and prove a difference exceptionality criterion analogous to the classical situation. We
also obtain a Galois correspondence for difference ring extensions in the style of Borceux-
Janelidze.
Along the way we explore the background of exceptional varieties, Grothendieck’s Galois
categories and discuss a proof of the classical exceptionality criterion. An overview of
difference algebraic geometry is given, motivated by the work of Tomaˇsi´
