Henri Poincaré publishes in 1895, in the Journal de l'École Polytechnique, "Analysis Situs", the paper founding algebraic topology as a systematic discipline. In it he introduces, among other central concepts, the fundamental group and simplicial homology, offers an early formulation of Poincaré duality, and coins the term "homeomorphism" itself. Poincaré would publish five supplements to the original work between 1899 and 1904; in the 1895 paper he initially conflates the concepts of homology and homotopy, a distinction he would only clarify in the fifth and final 1904 supplement, where he also formulates, in its closing lines, the question that would become known as the Poincaré conjecture: whether a closed three-dimensional manifold with trivial fundamental group is necessarily homeomorphic to the sphere. The conjecture would remain open for just over a century, until proved by Grigori Perelman in 2002-03.