  This paper takes its starting point in an idea of Grothendieck on the
representation of homotopy types.
  We show that any locally finite nilpotent homotopy can be represented by a
simplicial set which is a finitely generated free group in all degrees and
whose maps are given by polynomials with rational coefficients. Such a
simplicial set is in some sense a universal localisation/completion as all
localisations and completions of the homotopy is easily contructed from it.
  In particular relations with the Quillen and Sullivan approaches are
presented.
  When the theory is applied to the Eilenberg-MacLane space of a torsion free
finitely generated nilpotent group a close relation to the the theory of Passi
polynomial maps is obtained.
