A Note on Bimodules and $I{I}_1$-Subfactors

A brief introduction into bimodules of $I{I}_1$-factors is presented. Furthermore a version of the following result due to M. Pimsner and S. Popa is derived: Let $N=M_{-1}\subset M=M_0\subset M_1\subset M_2\subset \dots$ denote the Jones tower of a $I{I}_1$-factor $N\subset M$ with finite index. Then the factor obtained by the basic construction from the pair $N\subset M_{n-1}$ is equal to $M_{2n-1}$.