ISSN : 1226-0657
A Hilbert space operator T is a 2-isometry if <TEX>$T^{{\ast}2}T^2\;-\;2T^{\ast}T+I$</TEX> = O. We shall study some properties of 2-isometries, in particular spectra of a non-unitary 2-isometry and give an example. Also we prove with alternate argument that the Weyl's theorem holds for 2-isometries.
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