Some more on hyperfunctions - sec. 9.7

Roger Penrose says that according to the excision theorem the notion of a hyperfunction (f,g) is independent of the regions on which f and g are defined.

The excision theorem is an algebraic topology theorem that relates to cohomology groups on sheaves, or something like that. It is probably not very complicated at heart, but there's an "Introduction to the theory of hyperfunctions" by Hikosaburo Komatsu which has a more basic proof, using the Mittag-Leffler theorem in complex analysis. He uses a variant of the usual Mittag-Leffler theorem, explained in an obscure, dense (think London fog) book "An introduction to complex analysis in several variables" by Lars Hoermander.

Enjoy! Komatsu's explanation is quite lucid, almost light reading.

Attachment:

hyperfunction.gif

When Komatsu writes

I think what he means by

is the limit that F approaches as you go towards

in the

direction.