Is the guarantee valid if the guaranteed party guarantees the guarantor, or the guaranteed party vouches for the primary debtor?

Primary text

The guarantee is invalid if the original debtor (the guaranteed party) guarantees the surety (the guarantor), or if the primary debtor vouches for the surety. This is invalid because the guarantee necessitates obligating the debt onto the guarantor's liability, and since the debt is already incumbent upon the guaranteed party, it is impossible to obligate him a second time regarding the same matter. Furthermore, the original debtor is the foundation of this debt, and he cannot become a branch or secondary obligor concerning it.