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Ganea conjecture : ウィキペディア英語版
Ganea conjecture
Ganea's conjecture is a claim in algebraic topology, now disproved. It states that
: \text(X \times S^n)=\text(X) +1, n>0 \,\!
where cat(''X'') is the Lusternik–Schnirelmann category of a topological space ''X'', and ''S''''n'' is the ''n'' dimensional sphere.
The inequality
: \text(X \times Y) \le \text(X) +\text(Y)
holds for any pair of spaces, ''X'' and ''Y''. Furthermore, cat(''S''''n'')=1, for any sphere ''S''''n'', ''n''>0. Thus, the conjecture amounts to cat(''X'' × S''n'') ≥ cat(''X'') + 1.
The conjecture was formulated by Tudor Ganea in 1971. Many particular cases of this conjecture were proved, till finally Norio Iwase gave a counterexample in 1998. In a follow-up paper from 2002, Iwase gave an even stronger counterexample, with ''X'' a closed, smooth manifold. This counterexample also disproved a related conjecture, stating that
: \text(M - )=\text(M) -1 ,
for a closed manifold ''M'' and ''p'' a point in ''M''.
This work raises the question: For which spaces ''X'' is the Ganea condition, cat(''X'' × S''n'') = cat(''X'') + 1, satisfied? It has been conjectured that these are precisely the spaces ''X'' for which cat(''X'') equals a related invariant, Qcat(''X'').
==References==

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