MR0645985 Smith, Hal L. Hal L. SMITH An abstract threshold theorem for one parameter families of positive noncompact operators Fako de l'Funkcialaj Ekvacioj Japana Matematika Societo. Funkcialaj Ekvaciog. Serio Internacia 24 1981 141--153 http://fe.math.kobe-u.ac.jp/FE/Free/vol24/fe24-2-2.pdf http://fe.math.kobe-u.ac.jp/FE/FE_pdf_with_bookmark/FE21-30-en_KML/fe24-141-153/fe24-141-153.pdf http://www.ams.org/mathscinet-getitem?mr=MR0645985 fe24-141-153 1981 An Abstract Threshold Theorem for One Parameter Families of Positive Noncompact Operators SMITH, Hal L. SMITH, Hal L.
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