“…Finally, if (X, G) is a space of orderings, by a fan in (X, G) we understand a subspace V such that the space (V, G| V ) is a fan. Sheaves of spaces of orderings had been defined in [4,Chapter 8], where the original results are phrased in terms of reduced Witt rings, and recently studied in [1] and [3]. The definition of the sheaf that we use here is exactly the one taken from [3].…”