A continuous, constructive solution to Hilbert's 17th problem.
A note on linear preserves of ternary cubic forms
A real nullstellensatz and positivstellensatz for the semipolynomials over an ordered field.
Let K be an ordered field and R its real closure. A semipolynomial will be defined as a function from Rn to R obtained by composition of polynomial functions and the absolute value. Every semipolynomial can be defined as a straight-line program containing only instructions with the following type: polynomial, absolute value, sup and inf and such a program will be called a semipolynomial expression. It will be proved, using the ordinary real positivstellensatz, a general real positivstellensatz concerning...
A weak Hasse principle for central simple algebras with an involution.
An -algebra approach to Artin’s solution of Hilbert’s Seventeenth Problem
Using lattice-ordered algebras it is shown that a totally ordered field which has a unique total order and is dense in its real closure has the property that each of its positive semidefinite rational functions is a sum of squares.
Angeordnete affine Ebenen als Ebenen mit einem System von Halbgeraden, und euklidische Ebenen, die genau eine Anordnung besitzen.
Axiomatisations simples des theories des corps de rolle.