The class of operators of the form Σ_jλ_j φ_j ⊗ ψ̄_j

Abstract

Definition 1. Let φ and ψ be two given vectors in ℌ. The symbol

$$ \varphi \otimes \overline \psi $$

represents then a transformation on ℌ, whose defining equation is given by

$$ (\varphi \otimes \overline \psi )f = (f,\psi )\varphi $$

for f ϵ ℌ.