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Part of the book series: Progress in Mathematics ((PM,volume 346))

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In this chapter, we define the four numbers that rule the functional calculus properties of our elliptic operators and that will help us to describe the ranges of well-posedness of our boundary value problems. We study intrinsic relations between these numbers, using the machinery developed in Chap. 4.

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  1. 1.

    In fact, this case never occurs as we shall see later on.


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Auscher, P., Egert, M. (2023). The Four Critical Numbers. In: Boundary Value Problems and Hardy Spaces for Elliptic Systems with Block Structure. Progress in Mathematics, vol 346. Birkhäuser, Cham.

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