Prolongations in differential algebra
  We develop the theory of higher prolongations of algebraic varieties over fields in arbitrary characteristic with commuting Hasse-Schmidt derivations. Prolongations were introduced by Buium in the context of fields of characteristic 0 with a single derivation. Inspired by work of Vojta, we give a new construction of higher prolongations in a more general context. Generalizing a result of Buium in characteristic 0, we prove that these prolongations are represented by a certain functor, which shows that they can be viewed as `twisted jet spaces.' We give a new proof of a theorem of Moosa, Pillay, and Scanlon that the prolongation functor and jet space functor commute. We also prove that the $m^{th}$-prolongation and $m^{th}$-jet space of a variety are differentially isomorphic by showing that their infinite prolongations are isomorphic as schemes. 
Eric Rosen