#### Room 318

#### Hypergroups and subfactors

#### V. S. Sunder

##### IMSc

*This series of lectures is about something I did between 25 and *

30 years ago. (The reason for these lectures now is the insistence of my last

Ph.D. student Keshab.) This work started with the observation that the

collection of irreducible `bifinite bimodules over a $II_1$ factor' possessed a

group-like structure we shall refer to as `integral hypergroups'. Subfactors

`of finite depth' give rise to such hypergroups; while some finite hypergroups

give rise to subfactors of finite index. The first assertion above was proved

in the third of those three papers, while the second assertion was the content

of the first two.

Done