HenriPoincaré, a Frenchman, is called "the last generalist in the field of mathematics". In his great scientific legacy, there is a proposition of fundamental significance in algebraic topology, which is the "Poincare conjecture" that has puzzled mathematicians for a whole century.

Poincare put forward this conjecture in a set of papers published in 1904: "A simply connected three-dimensional closed flow is like an embryo on a three-dimensional sphere." Later, it was summarized as: "Any N-dimensional closed manifold that is homotopy with an N-dimensional sphere must be homeomorphic with an N-dimensional sphere." We might as well make a shallow analogy with two-dimensional examples: a rubber film without holes is topologically equivalent to a two-dimensional closed surface, while an inflatable balloon can be regarded as a two-dimensional spherical surface, and the points between them are one-to-one correspondence, while the adjacent points on the rubber film are still adjacent points on the inflatable balloon, and vice versa.