题目： Intersections of subcomplexes in non-positively curved 2-dimensional complexes
摘要：Let X be a contractible 2-complex which is a union of two contractible subcomplexes Y and Z. Is the intersection Y∩Z contractible as well? In this note, we prove that the inclusion-induced map π1(Y∩Z)→π1(Z) is injective if Y is π1-injective subcomplex in a locally CAT(0) 2-complex X. In particular, each component in the intersection of two contractible subcomplexes in a CAT(0) 2-complex is contractible.
题目：A brief survey on bordism and cobordism
摘要：Let M be a closed smooth manifold. It is an interesting question whether M is the boundary of certain compact manifold. This question leads to the origination of bordism theory. In this talk, we will give a brief survey on bordism and cobodism.
This talk is divided into three parts. In the first part, we will recall some basic definitions and properties. In the second part, we will review some classical results in bordism and cobordism. In the third part, we will discuss some selected topics and will collect some open problems.
题目：Width of knots
摘要：Width is a knot invariant first introduced by Gabai. In this talk, we will give a survey on recent studies of this invariant and discuss the relationship between the width of a satellite knot K and that of the companion J . In particular, We prove that w(K) is no less than where is the width of a knot, K is a satellite knot, J is the companion and n is the winding number. This is a joint work with Li Zhen-kun.
题目：Some algorithm problems around GL_d(Z)
摘要：I will introduce some algorithm problems in geometric group theory, especially those involving general linear groups GL_d(Z)
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