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*Algebraic Topology*. If someone has the book, could you please clarify the part of the proof when he says "If we perform the deformation retraction of [itex]X^n\times I[/itex] onto [itex]X^n\times\{0\}\cup (X^{n-1}\cup A^n)\times I [/itex] during the

*t*-interval [itex][1/2^{n+1},\, 1/2^n] [/itex], this infinite concatenation of homotopies is a deformation retraction of [itex]X\times I[/itex] onto [itex] X\times\{0\}\cup A\times I [/itex]." I do not understand how this follows. Thanks in advance.