  The theory of classical realizability is a framework in which we can develop
the proof-program correspondence. Using this framework, we show how to
transform into programs the proofs in classical analysis with dependent choice
and the existence of a well ordering of the real line. The principal tools are:
The notion of realizability algebra, which is a three-sorted variant of the
well known combinatory algebra of Curry. An adaptation of the method of forcing
used in set theory to prove consistency results. Here, it is used in another
way, to obtain programs associated with a well ordering of R and the existence
of a non trivial ultrafilter on N.
