Locally path connected implies path connected

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In summary, the problem is to prove that if a metric space X is locally path connected and E is an open and connected subset of X, then E is also path connected. This can be shown by considering the set Y of all points that are path connected to a fixed point x in E, and showing that Y is open. Then, by using the fact that if a point is path connected to two other points, those two points are also path connected, we can show that E-Y is also open. This leads to a disconnection of the space, proving that all points in E are path connected.
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Mosis
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Homework Statement


We say the metric space X is locally path connected (lpc) if all balls are path connected sets.

Suppose X is lpc and that E is an open and connected subset of X. Prove that E is path connected.

Homework Equations


A set is open if every point is an interior point. A set is connected if it cannot be written as the union of two open, disjoint, non-empty sets. A set is path connected if given any two points x,y in the set, there exists a path between them.


The Attempt at a Solution


None really. My professor suggested that for a fixed x, I consider the set Y of all y that are path connected to x and show that this set is all of E by somehow showing that if it were not, I could disconnect the space using Y and Y complement.

I just don't see the direction that this problem could take. Is it long? Is it short but requires ingenuity? What should I try to do? Where am I trying to end up?

Help, it's hard!
 
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  • #2
It's not hard and doesn't require any stunning ingenuity. You just have to think clearly. Can you show Y is open? The main ingredient you need is that if a,b and c are three points, and a is path connected to b and b is path connected to c then a is path connected to c. Now can you show E-Y (the set of all points in E that aren't in Y) is also open? That's your disconnection.
 

What does it mean for a space to be locally path connected?

Locally path connected means that for every point in the space, there exists a neighborhood around that point where any two points in that neighborhood can be connected by a path.

How is path connectedness related to locally path connectedness?

Path connectedness is a stronger condition than locally path connectedness. A space that is locally path connected may not necessarily be path connected, but a path connected space is always locally path connected.

Can a space be locally path connected but not path connected?

Yes, there are examples of spaces that are locally path connected but not path connected. One such example is the topologist's sine curve.

What are the benefits of a locally path connected space?

A locally path connected space allows for more flexibility in constructing paths and understanding the connectedness of the space. It also has important implications in areas such as topology and analysis.

How is locally path connectedness used in real-world applications?

Locally path connected spaces are used in various fields such as physics, engineering, and computer science. They provide a framework for understanding the connectedness and continuity of physical systems, as well as for developing algorithms and models for computational simulations.

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