Skip to main content
Jim Conant's user avatar
Jim Conant's user avatar
Jim Conant's user avatar
Jim Conant
  • Member for 14 years, 3 months
  • Last seen this week
comment
Classification of 1-dimensional manifolds (not second-countable)
Just a remark, but in addition to second countable, you also need to assume Hausdorff. Otherwise you get examples like the line with two origins.
comment
“Combinatorial” moves between cell complexes
To add to @RyanBudney's answer, there is an invariant called Whitehead torsion that obstructs whether two homotopy equivalent complexes are actually simple homotopy equivalent (related by standard moves).
comment
Examples of common false beliefs in mathematics
"Every manifold is homotopy equivalent to a compact one": if you want a connected counterexample, take an infinite connect-sum (which is not well-defined in the infinite case, but just choose one.) Or take the complement of a cantor set in $\mathbb R^n$ for a more sophisticated (and related) example.
comment
Examples of common false beliefs in mathematics
The line with two origins is a simple counterexample.
comment
Examples of common false beliefs in mathematics
@ChrisPressey I tried this out on someone who stubbornly refused to believe .99999...=1, and actually saw himself as standing up to the ivory tower mathematicians who believed infinity was real. (Ugh.) His response was: that 1-.9999...= 0.0̅1. I had to admit it was a clever, if meaningless, answer.
comment
Swimming against the tide in the past century: remarkable achievements that arose in contrast to the general view of mathematicians
A story I heard is that Stephen Smale proved that sphere eversion is possible for even dimensional spheres using vary general arguments, but there was so much doubt about his result that he went ahead and constructed a specific sphere eversion for the $2$-sphere.
comment
A conjecture about homotopy $S^1\times B^3$'s
Does "k-fold cyclic" mean "k-fold cyclic cover?"
comment
A knot in the solid torus and a Mazur manifold
Simple answer: the given knot is obviously homotopic to the knot with winding number $1$ and homotopy implies homology.
comment
Relation between the dimension of vector spaces and dimension of the space
Maybe I am misunderstanding the question, but could you not take $d=2,t=1$ and $A$ a rotation matrix? Then you could pretty much get whatever $m$ you want.
comment
Unnecessary uses of the axiom of choice
Doyle and Conway's division by three paper.
comment
Regarding the surgery construction in "A procedure for killing homotopy groups of differentiable manifolds" by Milnor
Indeed, one needs to identify collars rather than glue along the boundary in order to get a differentiable structure on the result.
awarded
awarded
awarded
awarded
awarded
awarded
comment
Examples of interesting false proofs
@nombre indeed. The problem is with the application of the result, not the result itself, that and loose language around quantification.
comment
Examples of common false beliefs in mathematics
Although a knot and its mirror image do cancel in the concordance group!
awarded
1 2
3
4 5
30