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Published online by Cambridge University Press: 20 November 2018
It is known that the Toeplitz algebra associated with any flow which is both minimal and uniquely ergodic always has a trivial ${{K}_{1}}$-group. We show in this note that if the unique ergodicity is dropped, then such ${{K}_{1}}$-group can be non-trivial. Therefore, in the general setting of minimal flows, even the $K$-theoretical index is not sufficient for the classification of Toeplitz operators which are invertible modulo the commutator ideal.