Prove that there is no polyhedron with exactly seven edges.
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Solution
From each vertex of a polyhedron, at least three edges emerge.
## Solution
If a polyhedron has four vertices, then it is a tetrahedron, which has six edges. Let the number of vertices of the polyhedron be no less than five. At each vertex of the polyhedron, at least three faces meet, meaning that at least three edges emerge from each vertex. Therefore, the total number of edges is no less than
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