Feldman - IP in PSPACE.

Lund, Fortnow, Karloff and Nisan and Shamir - PSPACE in IP.

Ben-Or, Goldwasser, Kilian and Wigderson - Defined MIP.

MIP - Separate provers - interrogation better.

Fortnow, Rompel and Sipser - MIP in NEXP.

Babai, Fortnow and Lund - NEXP in MIP.