  For given graph $H$, the independence number $\alpha(H)$ of $H$, is the size
of the maximum independent set of $V(H)$. Finding the maximum independent set
in a graph is a NP-hard problem. Another version of the independence number is
defined as the size of the maximum induced forest of $H$, and called the forest
number of $H$, and denoted by $f(H)$. Finding $f(H)$ is also a NP-hard problem.
Suppose that $H=(V(H),E(H))$ be a graph, and $\G$ be a family of graphs, a
graph $H$ has a $\G$-free $k$-coloring if there exists a decomposition of
$V(H)$ into sets $V_i$, $i-1,2,\ldots,k$, so that $G\nsubseteq H[V_i]$ for each
$i$, and $G\in\G$. $S\subseteq V(H)$ is $G$-free, where the subgraph of $H$
induced by $S$, be $G$-free, i.e. it contains no copy of $G$. Finding a maximum
subset of $H$, so that $H[S]$ be a $G$-free graph is a very hard problem as
well. In this paper, we study the generalized version of the independence
number of a graph. Also giving some bounds about the size of the maximum
$G$-free subset of graphs is another purpose of this article.
