We consider the complex ind-group $G=SL (\infty, \mathbb{C})$ and its real forms $G^0=SU(\infty,\infty)$, $SU(p,\infty)$, $SL(\infty,\mathbb{R})$, $SL(\infty,\mathbb{H})$. Our main object of study are the $G^0$-orbits on ...