I tried few cases and found any two spanning tree of a simple graph has some common edges. I mean I couldn't find any counter example so far. But I couldn't prove or disprove this either. How to prove or disprove this conjecture?

  • Assuming the weights of the graph are distinct, the edge with the minimum weight will be present in all the minimum spanning trees. – Gokul 2 hours ago
  • @Gokul minimum spanning tree? What?... – Mr. Sigma. 1 hour ago
  • Oh, apologies. I read the title as whether minimum spanning tree have common edges. – Gokul 1 hour ago
up vote 5 down vote accepted

No, it's not true that any two spanning trees of a graph have common edges.

Consider the wheel graph:

enter image description here

You can make a spanning tree with edges "inside" the loop and another one from the outer loop.

No, consider the complete graph $K_4$:

It has the following edge-disjoint spanning trees: enter image description here

  • 2
    Oh! Elegant. Why I couldn't come upon this solution. ':O. – Mr. Sigma. 44 mins ago

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