tailieunhanh - Báo cáo toán học: "Imbedding the irrational rotation C*-algebra into an AF-algebra "

Tuyển tập các báo cáo nghiên cứu khoa học ngành toán học tạp chí Journal of Operator Theory đề tài: Imbedding luân chuyển không hợp lý C *- đại số đại số-AF. | Copyright by INCREST 1980 J. OPERATOR THEORY 4 1980 201-210 IMBEDDING THE IRRATIONAL ROTATION C -ALGEBRA INTO AN F-ALGEBRA M. PIMSNER and D. VOICULESCU Let Ớ 6 0 1 be an irrational number and Ag the corresponding irrational rotation c -algebra . the cross-product of the continuous functions on the unit circle by the automorphism corresponding to the rotation of angle 2ttỡ . This c -algebra is simple and has a unique trace state T. It has been shown by M. A Rieffel 9 that for every a 6 0 1 fl Z ỚZ there is a projection p e Ag such that t p a and he conjectured that r p can take values only in 0 1 fl Z ỚZ and even more that the map Kg Ag - R induced by T establishes an isomorphism between the ordered group Kg Ag and the subgroup z 0Z of R. The group Kg Ag has also appeared in the context of A. Connes work 2 on operator algebras associated with foliations as the range of an index-map in the case of the Kronecker flow on the 2-torus. In the present note we construct an imbedding of Ag into an -algebra constructed by E. G. Effros and c. L. Shen 3 the A-group of which is z ỚZ. This has as a consequence the fact that r p e z 0Z for all projections p e Ag or somewhat stronger that the image of the homomorphism Ka A0 - R induced by T is contained in Z ỚZ thus confirming a part of the facts conjectured by M. A. Rieffel. This together with Rieffel s result implies that AO1 and Ao2 are isomorphic if and only if ti 02 1 f 2 . The irrational rotation algebra is generated by two unitaries w V e Ag such that u vu e2fli0u and every pair u V of unitaries in some unital c -algebra B satisfying u vu e27ti9K determines a -monomorphism iỊ Ag- B such that Ỷ ý V t r w u. This fact will be used in what follows. Let ữi a2 . a . be the continued fraction expansion of 0 see 8 . The tt th convergent equals flj a2 . a and p q may be computed recurrent-Qn ly by the formulae p npn-l Pn-2 n ỷ 2 with Pg 0 Pi 1 1 ln -1 Vn-2 n 2 with gữ 1 q aỵ. 202 M. PIMSNER and D. VOICULESCU For each rt G N let

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