Por Ilda Perez da Silva (FCUL - DM).

Oriented matroids are combinatorial abstractions of linear subspaces of  $ R^n$  that were introduced, in the late 1970's, independently, and in different ways, by several authors: R. Bland, J. Folkman, J. Lawrence, M. Las Vergnas. Oriented matroids unified, give new insights and produce new  results on different areas mathematics: graph theory, linear programming, convexity , topology,. algebraic geometry and statistics. I will do a brief introduction to oriented matroids focusing on some fundamental questions and recent results.