The present book offers an essential but accessible introduction to the
discoveries first made in the 1990s that the doubling condition is
superfluous for most results for function spaces and the boundedness of
operators. It shows the methods behind these discoveries, their
consequences and some of their applications. It also provides detailed
and comprehensive arguments, many typical and easy-to-follow examples,
and interesting unsolved problems.
The theory of the Hardy space is a fundamental tool for Fourier
analysis, with applications for and connections to complex analysis,
partial differential equations, functional analysis and geometrical
analysis. It also extends to settings where the doubling condition of
the underlying measures may fail.