a b s t r a c t Formal topology presents a topological space, not as a set of points, but as a logical theory which describes the lattice of open sets. The application to Hilbert's program is then the following. Hilbert's ideal objects are represented by points of such a formal space. There are general methods to ''eliminate'' the use of points, close to the notion of forcing and to the ''elimination of choice sequences'' in intuitionist mathematics, which correspond to Hilbert's required elimination of ideal objects. This paper illustrates further this general program on the notion of valuations. They were introduced by Dedekind and Weber [R. Dedekind, H. Weber, Theorie des algebraischen Funktionen einer Veränderlichen, J. de Crelle t. XCII (1882) 181-290] to give a rigorous presentation of Riemann surfaces. It can be argued that it is one of the first example in mathematics of point-free representation of spaces [N. Bourbaki, Eléments de Mathématique. Algèbre commutative, Hermann, Paris, 1965, Chapitre 7]. It is thus of historical and conceptual interest to be able to represent this notion in formal topology.1 Logically, such a quantification is a priori a Π 1 1 statement and it is analyzed in the form of a Σ 0 1 equivalent assertion. 2 Technically, the introduction of a point of a formal space corresponds to working in the sheaf model over this space, and the elimination of this point is achieved by the Beth-Kripke-Joyal explanation of the logic of this sheaf model. In most cases, this elimination can be carried out directly without involving explicitly the notion of sheaf models.
0168-0072/$ -see front matterIf φ * has the going-up or going-down property and is surjective, it is clear in terms of points that this implies K dim Sp(Z ) K dim Sp(V ). The following proposition expresses this implication in a point-free way.Proposition 4. If φ : Z → V has the going-up or going-down property and is injective and K dim V < n then K dim Z < n.Proof. We give only the proof for the going-up property (the going-down property follows by duality). Let a 1 , . . . , a n be an arbitrary sequence in Z . Since K dim V < n we can find v 1 , . . . , v n in V such that Proposition 16. The spectrum of the lattice group Div(R) [13] is the dual of the Zariski spectrum of R.Proof. The spectrum of Div(R) is shown in [13] to be isomorphic to the lattice of positive elements of Div(R), that is the finitely generated ideal of R, with the order I J if and only if there exists n such that I J n . This is equivalent to saying that J is included into the radical of I.Proposition 17. If R is a Prüfer domain then the center map φ : Zar(R) → Val(R) is an isomorphism.7 In the localization R[1/u i ] the ideal x 1 , . . . , x n becomes principal and equal to x i . 8 Dedekind himself thought that the existence of such an inverse was the fundamental result about the ring of integers of an algebraic field of numbers [1]. Theorem 25 shows that this ring is a Prüfer domain.9 The structure of lattice group was discovered by Dedekind and rediscovered i...