in general). Let $F^m$ denote the iterated frobenius map. If $E$ is a $G$-bundle on $X$ we an take its pullback $F^{m^{*}}(E)$ which will be a $F^{m^*}(G)$ bundle. We call this the $m$-th frobenius pullback. By twisting Spec $k$ by the frobenius map (which will be an isomorphism), we can define a $k$-structure on $F^{m^*}(X)$, $F^{m^*}(G)$ as well as $F^{m^*}(E)$. The $G$ bundle $F^{m^*}(E)$ on $X$ is the same as the one obtained by extension of structure group under the homomorphism $G \rightarrow G$ given by the $m$-th frobenius map.\
Clearly if the frobenius pullback of a $G$-bundle is semistable with respect to the pulled back polarization, then so is the original bundle. A semistable $G$ bundle may not however pullback to a semistable $G$-bundle. A $G$-bundle $E$ is said to be [**strongly semistable**]{} if all its frobenius pullbacks are also semistable.

The instability parabolic
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[\[The instability parabolic\]]{}

$~$ In this section we discuss the role of the instability parabolic which plays an important role in studying extension of structure groups in positive characteristic. We first begin by recalling some elementary notions and facts from Geometric Invariant Theory.\
Let $K$ be an algebraically closed field. Let $G$ be a 