On Pimsner Popa bases

In this paper we examine bases for finite index inclusion of $II_1$ factors and connected inclusion of finite dimensional $C^*$- algebras. These bases behave nicely with respect to basic construction towers. As applications we have studied automorphisms of the hyperfinite $II_1$ factor $R$ which are `compatible with respect to the Jones' tower of finite dimensional $C^*$-algebras'. As a further application, in both cases we obtain a characterization, in terms of bases, of basic constructions. Finally we use these bases to describe the phenomenon of multistep basic constructions (in both the cases).