Theoremintro
Handshaking lemma
In any undirected graph the sum of all vertex degrees equals twice the number of edges, so the number of odd-degree vertices is even.
In any undirected graph the sum of all vertex degrees equals twice the number of edges, so the number of odd-degree vertices is even.
About this page
The build computes these levels from the evidence in the repository. Each row says what the next level needs. Read what the levels mean.
| Ladder | Level | What the next level needs |
|---|---|---|
| Human proof | H0 no proof |
|
| Lean | L0 no Lean part |
|
| Visual | V0 none |
|
| Writing | W0 stub |
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