i'm interested in the spin group $Spin(4,1)$ wich correspond to the symplectic group $Sp(1,1)$. The only source that I could find about it was wikipedia (http://en.wikipedia.org/wiki/Spin_group). It seems that there is no general definition about what a indefinite symplectic group is. It would be helpful if someone could provide me a text (or a proof) where I could find how come $Spin(4,1)=Sp(1,1)$. Thanks alot to everyone.
For example Cornwell (Group Theory in Physics Vol II,page 392) says:
$Sp(r,\,s)=\{A\in\textbf{GL}(n;\,\mathbb C): A^T\,J\,A=J\:\:{\rm and}\:\: A^\dagger\,G\,A=G\}$, where $r+s=n/2$ and
$J=\left( \begin{array}{clc} 0 && I_{n\times n}\\ -I_{n\times n} \end{array}\right),\hspace{.5cm} G=\left( \begin{array}{clclc} -I_{r\times r}&&0&&0&&0\\ 0&&I_{s\times s}&&0&&0\\ 0&&0&&-I_{r\times r}&&0\\ 0&&0&&0&&I_{s\times s} \end{array} \right)$
And there is another definition tha involves quaternions... so, which one?