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I am trying to gain some intuition about retracts, deformation retracts and strong deformation retracts (see for definitions). We have that any strong deformation retract is a deformation retract and any deformation retract is a retract (of course, by definition). Also, it is easy to think in a retract which is not a deformation retract.

Which are some examples of deformation retracts which are not strong deformation retracts?

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See exercise 6 on page 18 of Hatcher's book. Note the difference in terminology to Wikipedia! – t.b. May 5 '11 at 21:56
Similar question to this one has been asked again and an answer can be found here. The same example but with more details can be found here. – Test123 Apr 27 '14 at 6:59

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