  Over-smoothing is a severe problem which limits the depth of Graph
Convolutional Networks. This article gives a comprehensive analysis of the
mechanism behind Graph Convolutional Networks and the over-smoothing effect.
The article proposes an upper bound for the occurrence of over-smoothing, which
offers insight into the key factors behind over-smoothing. The results
presented in this article successfully explain the feasibility of several
algorithms that alleviate over-smoothing.
