A vertex-induced subgraph (sometimes simply called an "induced subgraph") is a subset of the vertices of a graph 
together with any edges whose endpoints are both in this subset.
The figure above illustrates the subgraph induced on the complete
graph 
by the vertex subset 
. An induced subgraph that is a complete
graph is called a clique. Any induced subgraph of
a complete graph forms a clique.
The subgraph induced by a set of vertices can be computed in the Wolfram
Language using Subgraph[g,
vlist].
A graph is called a perfect graph if, for each of its induced subgraphs 
, the chromatic number
of 
equals the largest number of pairwise adjacent vertices in 
.
