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, $operatorname{GL}(n,mathbb{R})⋅alpha:={alpha(g^{−1}⋅,g^{−1}⋅):gin operatorname{GL}(n,mathbb{R})}$ 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 $operatorname{sym}(mathbb{R}^{n})$.