September 19, 2003 G.Khimshiashvili "Quaternions in some problems of low-dimensional geometry" We discuss the topological and geometric structure of certain differentiable mappings which are constructed using quaternions. For example, it turns out that, for a unilateral (i.e., variable commutes with the coefficients) quaternionic polynomials in one variable, the structure of its zero set can be described in a quite effective way. Related results about the structure of stable perturbations of a quaternionic branch point and some conjectures about the structure of stable perturbations of quaternionic polynomials will be also presented. It will be also shown that quaternions may be used for constructing analytic discs in loop spaces and conformal codimension one immersions of two-dimensional closed surfaces. Another two visual applications of quaternions are related to the so-called Weisbach's theorem (called sometimes the main theorem of axonometry) and to the description of configuration spaces of polygons in five-dimensional Euclidean space. --- http://www.pdmi.ras.ru/~lowdimma