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which maps of groups does this produce
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Reid Barton
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More generally, if A and X0 are any finite CW complexes, and f : A → X0 is any map, let Y be the mapping cone of f, and let X be Y with the cone point removed; then Y is the one-point compactification of X, and the inclusion X0 → X is a homotopy equivalence. (David's example is the case A = X0 = S1, f = id.) So any map X → Y which is the mapping cone of something is homotopy equivalent to a one-point compactification.

I don't think you can realize any map of groups as the induced map on π1 of a mapping cone (0 → Z/2Z?) but you can realize (G → 0, 0 → a free group, ...)

More generally, if A and X0 are any finite CW complexes, and f : A → X0 is any map, let Y be the mapping cone of f, and let X be Y with the cone point removed; then Y is the one-point compactification of X, and the inclusion X0 → X is a homotopy equivalence. (David's example is the case A = X0 = S1, f = id.) So any map X → Y which is the mapping cone of something is homotopy equivalent to a one-point compactification.

More generally, if A and X0 are any finite CW complexes, and f : A → X0 is any map, let Y be the mapping cone of f, and let X be Y with the cone point removed; then Y is the one-point compactification of X, and the inclusion X0 → X is a homotopy equivalence. (David's example is the case A = X0 = S1, f = id.) So any map X → Y which is the mapping cone of something is homotopy equivalent to a one-point compactification.

I don't think you can realize any map of groups as the induced map on π1 of a mapping cone (0 → Z/2Z?) but you can realize (G → 0, 0 → a free group, ...)

Source Link
Reid Barton
  • 25.2k
  • 1
  • 76
  • 133

More generally, if A and X0 are any finite CW complexes, and f : A → X0 is any map, let Y be the mapping cone of f, and let X be Y with the cone point removed; then Y is the one-point compactification of X, and the inclusion X0 → X is a homotopy equivalence. (David's example is the case A = X0 = S1, f = id.) So any map X → Y which is the mapping cone of something is homotopy equivalent to a one-point compactification.