The study of the general behavior of the iterates of measure preserving
functions on a measure space is called  ergodic theory.
The  problem has some interesting connections to ergodic theory, because
the function T extends to a measure-preserving function on the 2-adic
integers
 problem has some interesting connections to ergodic theory, because
the function T extends to a measure-preserving function on the 2-adic
integers  defined with respect to the 2-adic measure.
To explain this, I need some basic facts about the 2-adic integers
 defined with respect to the 2-adic measure.
To explain this, I need some basic facts about the 2-adic integers
 ,
cf. [14], [50].
The 2-adic integers
,
cf. [14], [50].
The 2-adic integers  consist of all series
 consist of all series
 
  where the
where the  are called the 2- adic digits of
 are called the 2- adic digits of  .
One can define congruences
.
One can define congruences  on
 on  by
by  if the first k 2-adic digits of
if the first k 2-adic digits of  and
 and  agree.
Addition and multiplication on
 agree.
Addition and multiplication on  are given by
 are given by
 
  The 2- adic valuation
The 2- adic valuation  on
 on  is given by
 is given by  and for
 and for
 by
 by  , where
, where  is the
first nonzero 2-adic digit of
 is the
first nonzero 2-adic digit of  .
The valuation
.
The valuation  induces a metric d on
 induces a metric d on  defined by
 defined by
 
  As a topological space
As a topological space  is compact and complete with respect to the metric
d; a basis of open sets for this topology is given by the 2- adic discs of radius
 is compact and complete with respect to the metric
d; a basis of open sets for this topology is given by the 2- adic discs of radius
 about
 about  :
:
 
  Finally one may consistently define the 2- adic measure
Finally one may consistently define the 2- adic measure
 on
 on  so that
 so that
 
  in particular
in particular  .
The integers
.
The integers  are a subset of
 are a subset of  ; for example
; for example
 
  Now one can extend the definition of the function
Now one can extend the definition of the function  given by (2.1) to
given by (2.1) to  by
 by
 
 