# Collinearity-Preserving Functions between Desarguesian Planes

**Book Synopsis Collinearity-Preserving Functions between Desarguesian Planes by : David S. Carter**

Using concepts from valuation theory, we obtain a characterization of all collinearity-preserving functions from one affine or projective Desarguesian plane into another. The case in which the planes are projective and the range contains a quadrangle has been treated previously in the literature. Our results permit one or both planes to be affine and include cases where the range contains a triangle but no quadrangle. A key theorem is that, with the exception of certain embeddings defined on planes of order 2 and 3, every collinearity-preserving function from one affine Desarguesian plane into another can be extended to a collinearity-preserving function between enveloping projective planes.

# Proceedings of the National Academy of Sciences of the United States of America

**Book Synopsis Proceedings of the National Academy of Sciences of the United States of America by : National Academy of Sciences (U.S.)**

# Rings and Geometry

**Book Synopsis Rings and Geometry by : R. Kaya**

When looking for applications of ring theory in geometry, one first thinks of algebraic geometry, which sometimes may even be interpreted as the concrete side of commutative algebra. However, this highly de veloped branch of mathematics has been dealt with in a variety of mono graphs, so that - in spite of its technical complexity - it can be regarded as relatively well accessible. While in the last 120 years algebraic geometry has again and again attracted concentrated interes- which right now has reached a peak once more - , the numerous other applications of ring theory in geometry have not been assembled in a textbook and are scattered in many papers throughout the literature, which makes it hard for them to emerge from the shadow of the brilliant theory of algebraic geometry. It is the aim of these proceedings to give a unifying presentation of those geometrical applications of ring theo~y outside of algebraic geometry, and to show that they offer a considerable wealth of beauti ful ideas, too. Furthermore it becomes apparent that there are natural connections to many branches of modern mathematics, e. g. to the theory of (algebraic) groups and of Jordan algebras, and to combinatorics. To make these remarks more precise, we will now give a description of the contents. In the first chapter, an approach towards a theory of non-commutative algebraic geometry is attempted from two different points of view.

# Notices of the American Mathematical Society

**Book Synopsis Notices of the American Mathematical Society by : American Mathematical Society**

# Abstracts of Papers Presented to the American Mathematical Society

**Book Synopsis Abstracts of Papers Presented to the American Mathematical Society by : American Mathematical Society**