Elliptic boundary reduction

A compact-cylinder calculation shows how a boundary measurement can miss an entire tangential direction. The general argument then reduces an elliptic interior equation with arbitrary boundary measurements to a pseudodifferential system on the boundary, retaining its graded orders, full Cauchy trace and both inverse errors.

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The reading includes complete compact-cylinder formulas, both regularity and smooth-error solvability implications, solved exercises, exact operator-block products and the radial correspondence between relative and compact-support symbol classes. It makes no characteristic-class index-formula claim.

This is a selected lesson with supporting proofs from Elliptic Operators & Boundary Problems.

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