EN
Let A: X → X be a bounded operator on a separable complex Hilbert space X with an inner product $⟨·,·⟩_{X}$. For b, c ∈ X, a weak resolvent of A is the complex function of the form $⟨(I-zA)^{-1}b,c⟩_{X}$. We will discuss an equivalent condition, in terms of weak resolvents, for A to be similar to a restriction of the backward shift of multiplicity 1.