Let $\alpha$ and $\beta$ be two real symmetric bilinear forms in $\operatorname{sym}(\mathbb{R}^{n})$, with signatures $(p_{\alpha},n_{\alpha},z_{\alpha})$ and $(p_{\beta},n_{\beta},z_{\beta})$.

Please, I would like to have some references or bibliography about *published papers* concerning to the following theorem:

**Theorem** $β∈\overline{ \operatorname{GL}(n,\mathbb{R})⋅α}$ if and only if $p_{\alpha}\geq p_{\beta}$ and $n_{\alpha}\geq n_{\beta}$.

Here, $\operatorname{GL}(n,\mathbb{R})⋅\alpha:=\{\alpha(g^{−1}⋅,g^{−1}⋅):g\in \operatorname{GL}(n,\mathbb{R})\}$ and $\overline{ \operatorname{GL}(n,\mathbb{R})⋅α}$ is the closure of $\operatorname{GL}(n,\mathbb{R})⋅α$ with respect to the usual (Euclidean) topology of $\operatorname{sym}(\mathbb{R}^{n})$.