Siburg, Karl F.2008-05-272008-05-272008-05-27http://hdl.handle.net/2003/2529910.17877/DE290R-15928We give two proofs of the two-dimensional Borsuk-Ulam theorem. One is completely elementary and does not use homology theory or the mapping degree, while the second one makes use of the recent theory of symplectic quasi-states.enPreprints der Fakultät für Mathematik;2008-11510preprint