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Tower of fields
In
mathematics
, a
tower
of fields
is a sequence of field
extensions
The name
comes
from such sequences often being written in the form
A tower of fields may be
finite
or
infinite
.
Examples
is a finite tower with rational,
real
and
complex numbers
.
The sequence obtained by
letting
F
0
be the
rational numbers
Q
, and letting
If
p
is a
prime number
the
p
th
cyclotomic
tower
of
Q
is obtained by letting
F
0
=
Q
and
F
n
be
the field
obtained by adjoining to
Q
the
p
n
th
roots of unity
. This tower is of
fundamental
importance
in
Iwasawa theory
.
The
Golod–Shafarevich theorem
shows
that there are infinite
towers
obtained by
iterating
the
Hilbert class field
construction to a
number field
.