Minima of decomposable forms of degree $n$ in $n$ variables for $n\geqslant3$

It is proved the theorem: if for any $X\in\mathbb{Z}^n$ ($X\ne0$) be $|F(x)|\geqslant\mu>0$ for factorable form $F(X)$ of degree $n$ in $n$ variables then $F$ is equal up to a constant to a integral form provided that $n\geqslant3$.