Incompleteness and nonexistence of a joining geodesic

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Give an example (e.g., draw a picture) to show that a connected surface can have two points which are not joined by any geodesic. What is the usual topological hypothesis that prevents this problem?

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References

[CJP+11] Chen J., Jiang G., Pan Y., Qin T., Tong Y., Wu Q., Xu S., Li T. Problems and Solutions in Mathematics. 2nd ed., World Scientific, 2011.