= Spectral Weyl sequence
{title2=$\|f_n\|=1,\quad(L-\lambda I)f_n\to0$}
For a bounded <self-adjoint operator> $L$, a spectral Weyl sequence at $\lambda$ consists of unit vectors $f_n$ with $\|(L-\lambda I)f_n\|\to0$. Such a sequence exists exactly at points of the <spectrum of a bounded operator>. If no sequence exists, the shifted operator is bounded below, with closed range and zero kernel. Self-adjointness then makes its range dense, so it is invertible. This spectral criterion is different from the equidistribution <Weyl criterion>.
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