Abstract:In 2002, Littlejohn and Wellman developed a celebrated general leftdefinite theory for semi-bounded self-adjoint operators with many applications to differential operators. The theory starts with a semi-bounded self-adjoint operator and constructs a continuum of related Hilbert spaces and self-adjoint operators that are intimately related with powers of the initial operator. The development spurred a flurry of activity in the field that is still ongoing today.The main goal of this expository (with the exceptio… Show more
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