A Spectral "schematization" of Homotopy Types
  Toen has interpreted the schematization problem as originally imagined by Grothendieck in "Pursuing Stacks" in such a way that solution(s) to this problem could be given. As he pointed out, there are many solutions available, and he gave two constructions solving this problem. What we do in the present work is reconsider what Grothendieck initially had in mind and develop a formalism that provides a concept of "schematization" and corresponding homotopy groups of "schematized" homotopy types. In our view this can be realized if we generalize topological spaces to symmetric spectra, and the mapping spaces Map(S,A) in the category of symmetric sequences play the role of homotopy groups, S the sphere spectrum, A a symmetric spectrum. 
Renaud Gauthier
math.AG math.AT