On commutativity of diagrams of type Π_1 factors

摘要

Such diagrams were first introduced and investigated by S. Popa (cf. [P1], [P2]) and, at present, this concept is linked in a natural way with numerous problems of subfactor theory. See, for example, [GHD], [K], [P3], [P4], [P5], [PP1], [We], [S], [Su], [SW], [WW], [Wi].