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    Post Made Community Wiki by Ivan Gundyrev

show/hide this revision's text 4 add example for locally compact case

Let $(X,d)$ be a metric space and $(\bar{X},\bar{d})$ its completion. There is a list of topological properties Wikipedia - Topological property

Does anybody know list which of them are retained (inherited) for completion? For example

  1. if $(X,d)$ is locally compact space then $\bar{X}$ may be non-locally compact space.(Consider the induced path metric space on the following subset of the Euclidean plane: $(0,1]\times {0} \cup (0,1] (0,1] \times { 1} \cup \bigcup_{n=1}^{\infty} 0 }\cup (0,1]\times {1/n} 1}\cup \times bigcup_{n=1}^{\infty}{1/n}\times [0,1]$.) 0,1] $.)

  2. if $(X,d)$ is separable space then $\bar{X}$ is separable space.

  3. if $(X,d)$ is connected space then $\bar{X}$ is connected space.
  4. if $(X,d)$ is path-connected space then $\bar{X}$ may be non path-connected space. (consider the graph of $sin(1/x)$ \sin(1/x)$ in the plane for positive $x$. )

I am interested in this problem in general, especially for the spaces with intrinsic metric.

show/hide this revision's text 3 add example for locally compact case

Let $(X,d)$ be a metric space and $(\bar{X},\bar{d})$ its completion. There is a list of topological properties Wikipedia - Topological property

Does anybody know list which of them are retained (inherited) for completion? For example

  1. if $(X,d)$ is locally compact space then $\bar{X}$ may be non-locally compact space.(Consider the induced path metric space .on the following subset of the Euclidean plane: $(0,1]\times {0} \cup (0,1] \times {1} \cup \bigcup_{n=1}^{\infty} {1/n} \times [0,1]$.)

  2. if $(X,d)$ is separable space then $\bar{X}$ is separable space.

  3. if $(X,d)$ is connected space then $\bar{X}$ is connected space.
  4. if $(X,d)$ is path-connected space then $\bar{X}$ may be non path-connected space. (consider the graph of $sin(1/x)$ in the plane for positive $x$. )

I am interested in this problem in general, especially for the spaces with intrinsic metric.

show/hide this revision's text 2 changed when X is path-connected
show/hide this revision's text 1