Number of connected components of a real variety and R-places

The purpose of this paper is to present results and open problems related to R-places. The first section recalls basic facts, the second introduces R-places and their relationship with orderings and valuations. The third part involves Real Algebraic Geometry and gives results proved using the space of R-places. Theorem14gives explicitly, in terms of the function field of the variety, the number of connected components of a non-empty smooth projective real variety. The fourth and fifth parts are devoted to the links with the real holomorphy rings and the valuation fans. Then we present an approach to abstract real places and conclude with some open questions. (C) 2020 Elsevier B.V. Tous droits reserves.