"Homotopia." . . "Obstrucció." . . "Obstructions, Théorie des Congrès." . . "Instituto de Matemática Pura e Aplicada (Brasil)" . . . . "Homologie." . . "Homotopie." . . "Obstruction theory." . . "Obstruction." . . "Homology theory." . . "Obstructions, Théorie des." . . "Déformation continues (Mathématiques)" . . "Homotopy theory." . . "Algebraic topology." . . "Obstruccions, Teoria de les." . . "Instituto de matemática pura e aplicada (Rio de Janeiro)," . . "Fibration." . . . . . . . . . . "Obstruktionstheorie"@en . "Obstruktionstheorie" . . "Obstruction Theory" . "Obstruction Theory"@it . . . . . . "Obstruction theory"@en . "Obstruction theory" . . . . "Obstruction theory ; y E. H. Spanier" . . . . . . . . . . . . . . . . . . . . . . . . . "Topologie algébrique." . .